Fonts are now also resolution independent.

- Added a mmToFontSize() method in Surface, its implementations and in
Screen.
- Use this method to compute the value to give to various text loaders.
- It is more practical to let this operation be chooses by the user,
and also allows to dynamically change fonts when the application switch
screens and the dpi change.
- Some fixes with Scissor.
- Passed from Jogl 2.1.0 to 2.2.0.