FRSKY emulation proof-of-concept working

Serial information exchanged between OpenLRS's modules (TX/RX) is now
agnostic to the user's selected telemetry protocol, serial packets will
be translated by the TX before being forward to the target endpoint
(i.e. OpenTX). FRSKY telemetry protocol can send well formed link
quality packets to OpenTX which are displayed on the telemetry screen;
currently the link quality packet is created on TX.h for debugging
proposes and in the future will be moved to the correct
telemetry_frsky.h file (tFrsky class).