Random backdrop color should be settable

Change-Id: I1a0e795287179350dadb02b4dc37d5a84c3e955d

qml/common/ArtImage.qml

@@ -11,7 +11,7 @@ Rectangle {
     property alias asynchronous: image.asynchronous
     property alias source: image.source
 
-    color: Qt.rgba(Math.random(255), Math.random(255), Math.random(255), 1.0)
+    color: globalSettings.randomBackdropColor ? Qt.rgba(Math.random(255), Math.random(255), Math.random(255), 1.0) : "black"
 
     height: width*nativeUtils.imageCollection.data(modelIndex, PictureModel.SizeRole).height/nativeUtils.imageCollection.data(modelIndex, PictureModel.SizeRole).width
     width: parent ? parent.width : 0

qml/main.qml

@@ -91,6 +91,7 @@ Item {
         property string artView: "Trivial"
         property string backdrop: "Swirls"
 
+        property bool randomBackdropColor: false
         property bool smoothArt: false
         property bool randomlyMirrorArt: false
         property bool commonFeed: true