TTF 2 FNT generation process.

I've realised that creating BitmapFonts on the fly from .ttf files adds quite some time to the loading, especially in Android if the fonts are big.

To solve this problem I've managed to change GenerateSkinMojo.java to create .fnt from .ttf files and pack them with the TexturePacker. The good part about this is that we can also apply TextureFilters to the .fnt that improve quite a bit the scaling/downscaling of the fonts in the game.

This pr does not change the old behavior of ExtendedSkin.java, we can still create BitmapFonts on the fly from .ttf files.