New LightTelemetry module.

This is a simple & lightweight one way telemetry protocol.
It's intended to be used for air to ground long range telemetry, can fit in 1200 bauds.
For now It's dedicated to Ghettostation antenna tracker. It will be extended in the future for ground OSD usage with additional frames.

LTM is for now one 18 bytes frames refreshed at 5hz ( 900bauds ).