Needs to be re-written

Allows parameter access from QML among other things

The derived class wasn’t really adding any capabilties

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

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

Subclass of QMessageBox which re-implements the static public
functions. There are two reasons for this:
1) The QMessageBox implementation on OSX does now show the title
string. This leads to message boxes which don't make much sense. So on
OSX we set title to text and text to informative text.
2) If parent is NULL, we set parent to MainWindow::instance. This
prevents message boxes which can go behind MainWindow

Using QFileDialog directly on OS X can hang intermittently due to Qt
bug.

This is the Pixhawk research board, not the PX4 production board.

Handy for testing without a real board

QSerialPort buffering too slow on Windows.

Conflicts:
	src/uas/QGCMAVLinkUASFactory.cc
	src/uas/QGCMAVLinkUASFactory.h