GUT test framework integration

[carmel4a]

Adds GUT framework.
Requires #60 to be merged first.

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Tests should inherit from MaszynaGutTest due to lack of wait_idle_frames() bitwes/Gut#675

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• Add compile_comands.json to .gitignore -> moved to Remove compile_commands.json from repo #62
• Add info about compile_commands.json to README.md -> Remove compile_commands.json from repo #62
• Fix bug related to order of unregistering Train/Commands -> Unregistering train fix + removal of incorrect sm42 engine #61
• Remove TestowySilnikElektryczny from demo SM42 -> Unregistering train fix + removal of incorrect sm42 engine #61

[carmel4a]

Please include GUT addon as a submodule (or something else)

@marcinn we need to discuss that, details on Discord.

[marcinn]

@carmel4a I'll split commits not related to GUT to a separate PR's. It is easier to maintain the project when PR's are as atomic as possible

[marcinn]

This branch requires #60 to be merge.

[marcinn]

@JezSonic I've made some crucial changes to the code initially proposed by @carmel4a:

• GUT added as a submodule
• Scons creates a proper copy of the GUT (not symlink) to the demo project
• There is a Dockerfile which is used by Github CI to run tests, but you can use it to run it locally, too (shortcut is in the Makefile)
• First tests are more accurate and fully useful - they're not just examples
• MaszynaGutTest adds wait_idle_frames helper, which isn't available in GUT but will be crucial for many of our tests
• I've added GitHub Action with caching docker image layers (but the image doesn't need to be pushed to any hub)

IMPORTANT NOTE: Before merging this PR a #60 should be merged first. I've built this branch top of reorganize-repo branch because of issues related to building the project. In the other words: this branch contains same commit as #60.

ALSO please note that this PR includes some fixes of the TrainController. The tests I added detected these issues! :)

[JezSonic]

Scons runned twice without need for that

[marcinn]

Must be run twice. Every docker build command creates a new layer (overrlayfs), which can be cached. First run is compiling godot-cpp. The second is compiling our code and linking them together, saving the result in a new layer.

[JezSonic]

I think that you can use cache from scons builds for Godot cpp there tho, so docker wont need to build it at all if the cache will exist

[marcinn]

Thanks!