Remove unused modeCount

Added Configuration Username
Report Login Error on incorrect configuration username/password 

Fix merge screwup

Support up to 64 buttons, not limit to 16
Send a single button command and not a stream of commands at 25Hz
Send button commands through signals (it's coming from a different thread)
Hide gimbal support through analog channels (there are no MAVLink messages to handle it)

Map gimbal controls
Keep track of gimbal position within Vehicle

Add gimbal to external control signal

Guard against no geometry being set

Add camera trigger
Add video start/stop/toggle recording
Add gimbal pitch and yaw

- Reimplement same behaviour as version 3.1 while resizing the window :
    Stretch the text area to fit the screen
- Change setting text from Alternate Instrument Panel to Vertical Instrument Panel

By default the Instrument Panel is the one from master,
It can be switched to alternate version by a checkbox in General Settings/Fly View

- Rename QGCInstrumentWidgetAlternate to QGCInstrumentWidget as it's now the default version
- Select  QGCInstrumentWidget as instrumentLoader source

The instrument widget layout is now a stack of :
- QGCAttitudeWidget
- Item that contain ValuesWidget
- QGCCompassWidget