Added a dialog asking the user about overwritting an existing file.

Tweaking the documentation for QFileDialog and replacing the doxygen "@" escape to be consistent with the rest of the code.

QGCApplication::saveTempFlightDataLogOnMainThread()
MainWindow::startVideoCapture()
QGCBaseParamWidget::saveParametersToFile()
QGCDataPlot2D::savePlot()
QGCDataPlot2D::saveCsvLog()
WaypointList::saveWaypoints()
QGCToolWidget::exportWidget()
LinechartWidget::startLogging()

Making sure defaultSuffix doesn’t start with a dot (i.e. “.bar”)

QGCFileDialog::getSaveFileName()

Assert if defaultSuffix contains a dot (i.e. “.bar”)

UnitTest::_getSaveFileName()

Added appropriate AcceptMode to AcceptSave so the OpenFileSave shows the proper Save button instead of the default Open button.

Revert premature assumption that adding support for selected filters in Open Save would not affect all other file dialog operations. As is, unit tests requires all or nothing.

WIP issue #1173. Adding default suffix (extension). While at it, added selected filter support and removed unit test assert about its use.

QQuickWidget can’t handle this

Now works for more than Serial links

Moving methods from MainWindow to QGCApplication so that more things
can run without a window. Helpful for testing.

Emitting signal beforehand can lead to subtle bugs where code expects
value to be updated and it is not.