Project generation warnings; TeaVM update

[czyzby]

• Adds warnings printed to the console after project generation.
  • Warns when GWT is chosen along with a non-Java language.
  • Warns when Kotlin coroutines are included when targeting the TeaVM platform.
• Updates TeaVM backend to the new group ID and library names.
• Removes File.separator usage as per previous PR comments.
• Separates TeaVM launcher into a builder (compilation setup) and a launcher (TeaVM main with application settings).
• Minor refactoring here and there.