Mobile QML UI: color the application header correctly

Also, this got broken after the Kirigami to verion 2.2 in main.qml.
So, set the header background color according to our theme setting.

Notice, that there is a remaining issue here. We could color the
text color in the header, but now, this seems impossible (or I
do not understand how and where to set this).

Signed-off-by: Jan Mulder <jlmulder@xs4all.nl>

mobile-widgets/qml/main.qml

@@ -18,6 +18,7 @@ Kirigami.ApplicationWindow {
 		minimumHeight: 0
 		preferredHeight: Math.round(Kirigami.Units.gridUnit * (Qt.platform.os == "ios" ? 2 : 1.5))
 		maximumHeight: Kirigami.Units.gridUnit * 2
+		background: Rectangle { color: subsurfaceTheme.primaryColor }
 	}
 	property alias oldStatus: manager.oldStatus
 	property alias notificationText: manager.notificationText