TextField - Editable repeat time for cursor movements

The properties keyRepeatInitialTime and keyRepeatTime should be public for personalization, and static for mantain the same behaviour for all the TextFiled and TextArea inside the game.
Code refactoring: moved static properties to the top
Merge pull request #2637 from bacca87/textfield1

TextField - Editable repeat time for cursor movements
Fixes #2648
Merge branch 'master' of https://github.com/libgdx/libgdx
Move cast to btRigidBody and fall back on new instance if not exists yet
Merge branch 'master' of https://github.com/Microbius/libgdx