Change the way back button works and apply an small refactoring

Test classes now return to main menu whenever back button or escape key
are pressed instead of close application. Also, SpawnBodiesTest now use
camera.unproject() method to translate event coordinates.
Add new comment
Updates android version to 0.2

This version include two more test, improved functionality, better
viewport for different resolutions and a new splash screen.
Change version code
Remove InputProcessor from SpawnBodiesTest

Old code was preventing back button to work.
Add an exit button
Apply an small refactoring over button creation method
Update README.md
README.md update, introducing the goal of the repo
Link to app added
Update README.md
Merge branch 'master' of https://github.com/Leakedbits/Codelabs.git