Say hello to QStaticConfiguration

This class offers a value/setValue interface much like QSettings.
Support QStaticConfiguration in the backends

The backend is now used by QStaticConfiguration so we have to emit its
valueChanged signal when a setting is changed and we also need to
make the category accessible from outside.
Add a module for QML

This is Qt.labs.settings working with QStaticConfiguration and is
used as a test bed for upstreaming QStaticConfiguration.