Pass argc, argv to the platform plugins.

Allow for parsing of X11-specific arguments like -display,
-geometry. Introduce overload of
QPlatformIntegration::create() with argc and argv
and provide default implementation that calls the old version
(for platforms that do not have argc, argv). Provide default
implementation for the old version returning 0 so that platforms
using the new API compile.
Prototypically implement -display in XCB.

Task-number: QTBUG-29396
Change-Id: I6a0e9271fad6e2d10f11b80393025ae3a3e36623
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>
Have QFileDialog use QUrl internally

When using the native dialog and through the helper, we use QUrl in
QFileDialog. It is preparatory work for having QUrl based methods on
QFileDialog interface itself.

Done-with: sean.harmer@kdab.com
Done-with: faure@kde.org

Change-Id: I61e99d498252241f38ec05724702a90ba050c4bb
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>