New QGCCanvas control to fix redraw bug

src/QmlControls/QGCCanvas.qml

+import QtQuick 2.2
+import QtQuick.Controls 1.2
+import QtQuick.Controls.Styles 1.2
+
+import QGroundControl.Palette 1.0
+import QGroundControl.ScreenTools 1.0
+
+/// Canvas has some sort of bug in it which can cause it to not paint when top level Views
+/// are switched. In order to fix this we ahve a signal hacked into ScreenTools to force
+/// a repaint.
+Canvas {
+    Connections {
+        target: ScreenTools
+
+        onRepaintRequested: arrowCanvas.requestPaint()
+    }
+}

src/QmlControls/QGroundControl.Controls.qmldir

@@ -9,6 +9,7 @@ QGCComboBox         1.0 QGCComboBox.qml
 QGCColoredImage     1.0 QGCColoredImage.qml
 QGCToolBarButton    1.0 QGCToolBarButton.qml
 QGCMovableItem      1.0 QGCMovableItem.qml
+QGCCanvas           1.0 QGCCanvas.qml
 
 SubMenuButton       1.0 SubMenuButton.qml
 IndicatorButton     1.0 IndicatorButton.qml