This function is called automatically when a QSettings object is destroyed,
so is rarely needed to be called explicitly.

There are still some cases where
a QSettings object is passed-by-reference, so there I left the sync() calls as
it's unclear how permanent those objects are and if they'd call sync() before
application shutdown

Fixes bugs with savings settings for the window state, theme, UAS-connected view, and low-power mode.
Also removes some unneccesary logic that attempted to handled unclean shutdowns, which I haven't
been able to reproduce.

It was a poor proxy for better coding around the problem of bad settings or the lack of
settings on first-run.

No functionality changes in this code, just code clarify improvements.

Remove signal overrides

QGCFileDialog can now be handled by unit test code

Turn off Windows Error Reporting for unit tests

This keeps TeamCity from hanging on a dialog box

Remove unused code

This was leftover from a problem I was having with virtual slots

Simple MainWindow Unit Test

Splash screen is optional. Also remove some unused class definition.

New Unit Testing framework

Deployment target is still 10.6

Allows for UI unit tests to be written:
- Ability to respond to expected message boxes
- Ability to fail test if unexpected message boxes occurs