Updated to defines to align with FrSkySPort.h plus a few other misc changes

1) Reordered defines.  Add a few missing defines that might be useful.
Changed SENSOR_ID_FLVSS to A1, I think this is correct see FrSkySPort.h at github.com/opentx/opentx.

2) Added DEBUG_AVERAGE_VOLTAGE to enable/disable "Number of samples for
voltage average" message in release build.

3) Added support to debug base and custom mode