Add KTX project template

[czyzby]

Migrate and refactor @DavidPartouche's KTX template from the original gdx-setup to gdx-liftoff.

Kotlin files:

• ktxTemplate.kt
• ktxClassic.kt

Relevant commits:

• czyzby/gdx-setup@7df7076
• czyzby/gdx-setup@6422867
• czyzby/gdx-setup@a7524a7