Removed the ICONDIR token from the CSS styles; it wasn't necessary and slowed down applying new styles to QGC.

Hotfix: Fixed widget / UAS initialization order which led to text messages (and other updates) being ignored if the widget was not open when the UAS was created

Selecting the desired stylesheet now works correctly, including saving settings between application launches.

Reworked the styling UI. Now there are 4 options: light, dark, custom_light, and custom_dark. Things don't quite work right, but the proof-of-concept is done.

Further styling changes to the outdoor stylesheet. The indoor sheet was modified as inline styles are removed from the C++ code.

Some .ui files still pointed to an old mavground.qrc file. They now point to the proper qgroundcontrol.qrc file.

Removed commented-out references to setStyleSheet(). Moving towards all styles being set in .css files

Added missing separater to Tool Widgets menu.

Changes for new calibration in APM 3.0 (Re: https://github.com/diydrones/MissionPlanner/issues/38), and change in some of the serial timeouts

Addition of requesting status updates from APM, if APM is in a state with no status updates, this will request them