Rover: show modes as strings in log
Plane: show modes as strings in log
AP_AHRS: added _kp gain reduction for catapult launch

this should reduce the tendency of aircraft to nose down hard on
initial launch at high g
Plane : AP_L1_Control : Replaced division by constants with multiplies and adjusted default L1 period to 25 seconds
AP_GPS: move byte swapping code to cpp
AP_GPS: added last_message_time_ms() API

used to help GPS logging
Plane: log GPS messages as they come in

stops us logging duplicate messages
Rover: log GPS packets as they come in
Plane: log mode number as well as mode string

this makes graphing mode changes easier
Rover: log mode number as well as mode string

this makes graphing mode changes easier
autotest: changed mavlink log names to *.tlog

easier to view in MP