AP_Common: moved map_baudrate() into AP_Common

this version supports a much wider range of baudrates
GCS_MAVLink: moved main update() routine into GCS_Common.cpp

this fixes a common timeout error with loading large missions, and
means less per-vehicle code
Plane: changed baudrate parameters to 16 bit
Plane: update baud rate parameter descriptions
Plane: updates for new GCS_MAVLink API
Copter: change baudrates parameters to 16 bit
Copter: update baud rate parameter descriptions
Copter: updates for new GCS_MAVLink API
Rover: change baudrates to 16 bit

allows for much higher serial baud rates
Rover: update baud rate parameter descriptions
Rover: updates for new GCS_MAVLink API
AntennaTracker: updates for new GCS_MAVLink API