Compass Calibration: Added signals for IMU messages
Compass View: Fixes #403: Calibration for second compass (when available)
Compass View: Set all Offsets to 0
Compass View: Refactor all offset related ‘guard code’
Compass View: Fix layout in Message Box
Dev Env: Scripts to switch between Qt5 and Qt4
Merge remote-tracking branch 'upstream/master' into 274