Power over USB added to Brainboard

Brainboard can now be powered over USB by shunting a header behind the
USB connector. A diode connects 5V_USB to the 5V net.
Auxiliary Boards PCB Updated

Silkscreen on AuxBoard1 includes Cat5 color while AuxBoard2 now has M3
mounting holes and GND plane.
Schematics have also been cleaned up.