* LTM: Update LightTelemetry protocol to version 2.

It knows use 3 different frames at the selected rates:

Baudrate  1200 | 2400 & more
GPS       2Hz  |  5Hz
Attitude  5Hz  | 10Hz
Sensors   2Hz  |  5Hz

 G Frame (GPS position) (2hz @ 1200 bauds , 5hz >= 2400 bauds): 18BYTES
 0x24 0x54 0x47 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF  0xFF   0xC0
  $     T    G  --------LAT-------- -------LON---------  SPD --------ALT-------- SAT/FIX  CRC
 A Frame (Attitude) (5hz @ 1200bauds , 10hz >= 2400bauds): 10BYTES
 0x24 0x54 0x41 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xC0
  $     T   A   --PITCH-- --ROLL--- -HEADING-  CRC
 S Frame (Sensors) (2hz @ 1200bauds, 5hz >= 2400bauds): 11BYTES
 0x24 0x54 0x53 0xFF 0xFF  0xFF 0xFF    0xFF    0xFF      0xFF       0xC0
  $     T   S   VBAT(mv)  Current(ma)   RSSI  AIRSPEED  ARM/FS/FMOD   CRC