This fixes a bunch of bugs with setting the title for widgets, deleting
widgets, etc.  It also reduces the amount of code duplication, which is
always a good thing.

The JoystickWidget now has a parent so that it gets cleaned up when the MainWindow is closed preventing zombie-dialog syndrome.

The JoystickWidget now has a parent so that it gets cleaned up when the MainWindow is closed preventing zombie-dialog syndrome.

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

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

Change so MainWindow handles its own deletion, and deletion of other UI objects to allow for closing when the MainWindow is closed, regardless of if other windows are open.

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