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

Remove unused code

Link manager unit test and fixes

Fix linux compiler warning

Largest change is that once a link is added to LinkManager it maintains
ownership and is responsible for delete. If you need to delete a link
use LinkManager::delete. Also added guard code to assert if a Link is
deleted outside of LinkManager.

Allows you to run a single unit test from the command line

Singletons tracked by QGCApplication

- allow unit tests to use QGCApplication
- clear global singletons for each unit test run