Update documentation for the ECSS definitions

Group Services and ECSS Definitions into a doxygen page

Logging

This adds a Logging "library" to the ECSS Services repo. This library allows logging messages with different severities, and allows the user of the services to choose which severity they want displayed.

A comparison between [Google (glog)](https://github.com/google/glog), [spdlog](https://github.com/gabime/spdlog), [plog](https://github.com/SergiusTheBest/plog) and [Boost::Log](https://www.boost.org/doc/libs/1_63_0/libs/log/doc/html/index.html) was made, and we decided to go with a custom lite solution, also compatible with `etl::string`.

The following log levels are supported, but they are up for discussion:

|Level|Description|
|---|---|
| **trace** | Very detailed information, useful for tracking the individual steps of an operation.|
| **debug** | General debugging information.|
| **info** | Noteworthy or periodical events.|
| **notice** | Uncommon but expected events.|
| **warning** | Unexpected events that do not compromise the operability of a function.|
| **error** | Unexpected failure of an operation.|
| **emergency** | Unexpected failure that renders the entire system unusable.|
| **disabled** | Use this log level to disable logging entirely. No message should be logged as disabled.|

The library uses `#define`s that allow logging in this way:
```c++
LOG_ERROR << "Configuration not found";
LOG_INFO << "The camera took " << 15 << " pictures today";
LOG_DEBUG << "Ran function " << functionName << " with " << getId(functionName);
```

Closes #18.

It is lite enough to be used [on a microcontroller](https://gitlab.com/acubesat/obc/mockup-4/commit/4aaa55bb72030cee6cf4eca7b082297cf60edf37).

**See https://acubesat.gitlab.io/obc/ecss-services/docs/classLogger.html for more detailed documentation of the Logger functionality**.


The following images show a sample log output on x86 and on an MCU via UART:  
![Log output on x86](/uploads/2ed78e90bfbab8125879fe96346aa9c9/Image_Pasted_at_2019-8-8_14-04.png)![Log output on MCU](/uploads/c8505fc7f282ed520f36d5f4f2beabc7/Image_Pasted_at_2019-8-9_00-45.png)

See merge request acubesat/obc/ecss-services!44

Use a non-templated version of etl::string

Set the etl format as a static variable for the Logger

This prevents wasting time recreating the format variable every time the
LOG function is called.

Force inlining the LOG function

This forces the compiler to check the `if constexpr` structure, and
disable the logging line entirely if needed.

Never redefine the log level

Move `disabled` logging level to ease level checks

Thanks @xlxs41 for the suggestion!

Reinstantiate log level checks

Fix documentation, as suggested by @thodkatz

Add a few more documentation lines to LogEntry

Fixes for cppcheck-misra and vera checks due to updates & false positives

Apply suggestion to inc/Logger.hpp

Be explicit about the type used in the LogLevel enumeration

This makes LogLevel an unscoped strongly-type enumeration, making sure
there is consistency between the expected log level of uint8_t

Thanks @xlxs41 for the suggestion!

Fix a bug with error names not showing up in the logs

Take care of MISRA and vera++ concerns

Add the function that stores the logs

Switch order of execution to improve performance

Fix the build

CI pipeline optimization

Resolves #46 and #40.

The average pipeline time is ~11 minutes until failure or success with the current CI configuration. Main causes of this are:
- The original Docker image used for the runners (`lycantropos/cmake`) is bloated, weighing at about **600 MB** for the [latest tag](https://hub.docker.com/r/lycantropos/cmake/tags). This image is downloaded for every stage of the pipeline separately, and due to its size, there is a huge delay between setup and start of the stage.
- There are too many calls to `apt-get update` and `install`, that are executed at every stage without reason. Plus, downloading and installing additional packages *for every stage* is also time-consuming, which contributes to the delays.

This problem is solved by creating a lighter Docker image (`lightspot21/acubesat-ci`), based on Alpine Linux, which contains all the necessary tools for linting and building (`cmake`, `cppcheck`, `clang-tidy`, `gcc`, `vera++`) plus the code coverage tools `gcovr` and `lcov`. The whole package weighs at **168 MB** for the [latest tag](https://cloud.docker.com/repository/docker/lightspot21/acubesat-ci/tags), which is **73%** less than what we use currently.

Gains:
- Average pipeline time down to **5-7 minutes** from 11-13 (variation is due to server load) with some times even earlier when failing, resulting in quicker fixes.
- Ability to directly control tool versions.

All comments/ideas are welcome, especially on optimizing the Docker image size even more!

See merge request acubesat/obc/ecss-services!51

Reenable clang-tidy on new pipeline

Fix vera and clang-tidy

Update the used Dockerfile to include clang-tidy

Clean up commented out stuff from CI configuration

Update Dockerfile according to suggestions

Fix the virtual package

Move update to initialization to ensure latest version of everything

Merge branch 'faster-ci' of https://gitlab.com/acubesat/obc/ecss-services into faster-ci

Fixes for new broken clang-tidy rules

# This is the 1st commit message:
Add the Dockerfile used to generate the image
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Reenable clang-tidy on new pipeline
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Fix vera and clang-tidy
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Update the used Dockerfile to include clang-tidy
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Clean up commented out stuff from CI configuration
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Update Dockerfile according to suggestions
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Fix the virtual package
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Move update to initialization to ensure latest version of everything

Fix missing script directive

Update .gitlab-ci.yml

Override image entrypoint to include '-c' argument

Revert previous override due to broken .gitlab-ci.yml

Remove -Werror argument

Update .gitlab-ci.yml

Since main.cpp only refers to desktop content

Update doxygen configuration

See merge request acubesat/obc/ecss-services!42

A small string overhaul

This commit adds functions to:
- Append strings of fixed size
- Read strings with or without a trailing `\0`

There is also a string-related fix for the function management service.

This takes care of issues #43 and #11.

Don't mind the irrelevant commits, they show up because `ci-1` is not merged to master yet.

See merge request acubesat/obc/ecss-services!41

Fix cppcheck errors

Fix pipeline issues.

See merge request acubesat/obc/ecss-services!43

Fix the build

This MR:
- fixes a regression with the new version of cppcheck (`1.88`) on some testing code
- disables the 13.4 MISRA rule due to a false positive
- removes the clutter created by .dump files

See merge request acubesat/obc/ecss-services!40