Instead us a Toolbox concept which hangs off of QGCApplication

They were causing variable scoping conflicts. This in turn caused the
widget to not update. Active property is not needed since the handling
of active/inactive vehicle is handled outside of the control

Updated existing icon and added a new one for when things have changed.

Also handling the toggling of the various panes on the right side of the screen to match the current selected task.

Adjusted icons so they no longer contain a background.
Added *Exclusive* functionality to the RoundButton element.
Added OnClicked signal for the drop down boxes so I could turn off Add Mission Item and Home Mode.