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

- 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

Do not dynamic cast or de-reference QObject, since object is either in
destructor or may have already been destroyed.

Destroyed signal must have been working incorrectly in the past.

Make sure to no de-reference already deleted object

This allows you to determine if full parameter list is ready if you
missed the parameterListUpToDate signal.

This allows you to determine if full parameter list is ready if you
missed the parameterListUpToDate signal.

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

This removes double emit of signals.

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

Also fixed typo in offline waypoint editing message.