Allow plugin to define default font size, toolbar height and option to display/hide plan view selector.

- Shot Interval in Survey
- Much change to time/distance calc

This makes text show up better on map images

Prevent shutdown ordering crashes

* Make MainToolbarIndicators reusable by other views
* Change to font based ratio sizing

Shows horizontal/vertical scroll indicators

Made QGCCorePlugin derive from QGCToolBox and expose everything through the same mechanism as everything else.

Conflicts:
	src/MissionManager/GeoFenceController.cc

This makes it available on mobile builds

_finalize methods need information which is not available if all you
have is a mavlink_message_t

-fixes #4035