Add Godot-requiring unit test support

[hhyyrylainen]

to fully compliment how Thrive can be automatically tested,

For potential approaches we can check what others have done: godotengine/godot-proposals#432

Before closing this issue the CI should be made to run the tests.

[hhyyrylainen]

Some unit tests could be made just by making the settings available when testing.

[hhyyrylainen]

This is done but the tests are disabled for now due to a bug in the testing library: MikeSchulze/gdUnit4Net#166

[hhyyrylainen]

This should now just be waiting for a new release of gdUnit.