[ins] properly define INS_VFF_R_GPS

closes #741
[electrical] min bat level check

This allows for detecting when voltage is too low to be a real reading and treats it as invalid.
The GCS shows BAT LOW INVALID.
The ap does not set bat_low or bat_critical if the reading was never valid.
But once a valid voltage is read then low level checking is always done.

closes #745
[fixedwing] stabilization adaptive: remove obsolete declarations

Thanks Loic.
[server] try to update AGL even if GPS is lost

close #742
[tools] flash via bmp: reset and detach from target after uploading

closes #746
[modules] Fix include related to stabilization_attitude in gain_scheduling to
reflect current file nomenclature.
[gcs] Display AP mode forward (FWD) when selected instead of UNK
[mesages] Display AP mode FORWARD when selected instead of just uint
value