2nd revision

Second revision of ORbit16(tm) PCB is ready.

Major modifications:
- removed resistors from ICSP line
- added a DPDT switch for USB HOST/Device selection. The switch now is near a border of the PCB so it's easy to commutate even if there's a shield mounted on
- improved ground planes
- improved thermal pad for voltage regulators
- new silkscreen: now is more easy to use pins without having documentation on hands
- usb host connector now is centered

I hope can send the pcb to a good pcb manufacturing service.