Line chart widget: Auto-force ground time if offset is more than 3 seconds (30% of default view width)

Fixing braces
Changing data plot save files to csv only
Fixing LinechartWidget::startLogging() as it no longer needs to worry about a proper file name being set.

Changing the order of the QGCFileDialog::getSaveFileName() function. The idea was to expand the existing QFileDialog version but as we removed the selectedFilter, we might as well make this more intuitive. The options argument is the one trully optional and should be last.
Adding an example to the documentation on how to go about figuring out what file type was returned by these functions.

Removed the “selectedFilter” argument from the QGCFileDialog functions along with references to it in unit tests.
Fixed function declarations and prototypes formatting while at it.
Changed the caption of a few file save dialogs with a more descriptive text (explicitly telling what is being saved).

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()

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

This makes unit test output easier to read

This makes unit test output easier to read

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

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.

I don't think it's needed anywhere in QGC since this has been a bug for a long time.

I was unsure how to update the QwtPlotPrintFilter code, so I just commented it out with a FIXME.

MainWindow::loadDataView has been commented out for 9 months now.
Removed commented out code instead of leaving cruft in.

There's no need to create multiple signals - connect() is fine with
connecting styleChanged(MainWindow::QGC_MAINWINDOW_STYLE)  to a slot
with no parameters.