lib: Added footprint for 25 pin header.
lib: STM32F4-64: Renamed invalid PB16 to PB15.
mcu-board-stm32f4: Reverse voltage protection.

Added FET for reverse voltage protection to 3V line. 5V line is
assumed to be protected by the regulator.

Added FET to disconnect the external power pin from the USB VBUS
sense pin to allow high voltages from the external pin. The TLV70133
supports up to 24V input.

Moved crystal capacitors closed to crystal pads.