Legacy code cleanup

[czyzby]

• [x] Remove excessive @author annotations from KDocs.
• [x] Change package from legacy com.github.czyzby.setup to gdx.liftoff.
• [x] Remove customs forks of gdx-lml libraries.
  • [x] Decouple custom fork of gdx-lml libraries from any application-specific code.
  • [x] Submit gdx-lml bug fixes to crashinvaders/gdx-lml.
  • [x] Switch to the crashinvaders/gdx-lml fork.
• [x] Add Kotlin linter. Format code.
• [x] Add @Suppress("unused") annotations for methods, classes and fields accessed via reflection.
• [x] Add contribution guide.

[czyzby]

@tommyettinger Outside of updating gdx-lml to the latest libGDX version, do you recall any significant changes to libraries fork that would prevent from simply switching to @crashinvaders fork? I was able to remove the local Java sources and run the application using the new fork seemingly without any issues after decoupling InterfaceService from Configuration.

[czyzby]

It seems that a bug related to a crash when using markup does not occur after replacing local gdx-lml fork with CrashInvaders version. I think there's no need to apply the local changes of gdx-lml to the CrashInvaders fork.