Partway through refactoring of UAS deletion. This is in order to actually support removing UASes from QGC, which is currently impossible.

Refactored QGC startup so that MainWindow::instance() is usable everywhere. This was required to get the styling working properly for ChartPlot.

A few more style updates. Added theme awareness to the toolbar. Also switched the plot zoomer over to use blue instead of red as it's selector coloring to match the standard accent color for QGC.

The light and dark themes now use slightly different blues for their accent colors that is higher contrast.

Curve colors are only displayed when curves are being plotted. Also fixed bug when generating CSS coloring from color.

Further consolidation of Plot code into ChartPlot. Also removed some unused variables from LinechartWidget.cc. Also only active curves are recolored in the IncrementalPlot class.

Moved all shared code for IncrementalPlot and LinechartPlot into a common ChartPlot superclass. Also recoloring the background of both widgets now works when switching between color schemes.

The background color of the mission items is now controlled by stylesheets as well. This change also fixed restyling the mission lists when a style change occurred.

The HUD is now theme-aware. Unfortunately it still has some coloring bugs and doesn't support changing themes at runtime. Not sure if the latter is a show-stopper however.

Fix for crash involving serial links not being removed from QGCToolBar

Reworked the UAS listing. It's organized differently and styled differently. Also the fading of the heartbeat status now works properly. Also fixed some theming issues with the connectButton when it was checked.

Synchronized the dark theme to the changes to the light theme from the last commit. Also made more text change color based on selected theme.

More vehicle config

Extended most of the new toolbar theming to the dark theme. It looks pretty good, though both themes still need some more refinement.

The toolbar now displays much nicer under the light theme. Also colorized the connect/disconnect & delete buttons in the communications settings window.

Whoops. Look like you can't inherit from QToolBar using Qt Designer. Restored last set of code. Also, changed one of the QToolButtons to a QLabel in QGCToolbar.

Waypoint and compile fix

Fix for static const float cannot be initialized within a class definition, and other windows compile errors.

Fix for bug where displaying WaypointList after adding offline waypoints resulted in an empty waypoint list, until the next waypoint was manually added