CoronaBitmap - slight navigation improvement

[romullus]

I think navigation between offset and tiling U/V fields by using tab / shift-tab or arrow keys might be improved. In native bitmap loader it is working like this: offset U <-> offset V <-> tiling U <-> tiling V which makes to do changes in say tiling very easy. In CoronaBitmap however it works differently: offset U <-> tiling U <-> tiling mode U and offset V <-> tiling V <-> tiling mode V I found it way less convenient.

[Ondra]

done