New image decodification modules & IO devices

Modules:
 - cellPngDec added.
 - cellJpgDec added.
 - cellGifDec added.

IO:
 - Keyboard (cellKb* / libkb) support added.
 - Mouse (cellMouse* /libmouse) support added.

GUI:
 - Changed layout of Settings menu.
 - Added the new IO handlers to Settings menu.