Rename BouncingBall to BouncingBall

This class now represents a Test of the Codelabs and has a variable to
set its name.
Three new classes to maintain a list of all test and work with them
New json file to load skin definitions
Add assets used by the main menu
Add an exclusion for desktop assets folder that is indeed a link
New class to show a simple menu with buttons to all tests
Remove an unused import
Fix viewport size in large devices
Change title and icon in Android app
Add splash screen
Change desktop app resolution to 800x600
Fix viewport on old Test to adapt them to different resolutions
Add new test (SpawnBodiesTest) to box2D collection

This test spawn a new body every time the user touch the screen (limited
to 20 bodies).
Remove auto generated comments
Add new test (DragAndDropTest) to Box2D collection

This new test shows how to use MouseJoint to drag and drop bodies.
Change first screen to Splash screen instead of MainMenu
Reduce splash screen duration to 4 seconds
Small refactoring on create methods
Merge branch 'master' of https://github.com/Leakedbits/Codelabs.git