Telemetry

The periodic telemetry system using a register mechanism that allows to get rid of the old macro style (easier debugging).
The send functions are now in different files, close to the data they are sending through the telemetry (as much as possible at least).

Things to improve:
 - send error report when trying to register unknown message
 - send error report when trying to send a message that has not been registered
 - find better names here and there
 - some message don't have a nice place yet (like BARO_RAW...)