Beginning of the great GPS unfucking.
* Proper initialization sequence framework for various supported GPS types. NMEA will now auto-detect its baud rate based on received frames.
* As a result of the above, gps_baudrate has been changed to enum, to only allow fixed rates. (GPS baudrate, -1: autodetect (NMEA only), 0: 115200, 1: 57600, 2: 38400, 3: 19200, 4: 9600)
* UBX binary initialization at any specified baudrate with auto-reconnect on signal loss.
* GPS thread to handle initialization, signal loss and configuration. No longer does GPS need to be powered before FC, and on GPS reconnect, it will be re-initialized if needed.
MTK NMEA/binary initialization is omitted for now, as I can't find my MTK GPS
GPS deltaTime can be calculated to display update rate.


git-svn-id: https://afrodevices.googlecode.com/svn/trunk/baseflight@438 7c89a4a9-59b9-e629-4cfe-3a2d53b20e61