Many fixes for XAML Designer...

- Outline Treeview uses now SharpTreeView
- OutlineTreeView Context Menu
- OutlineTreeView Show/Hide Elements
- DesignSurface is now a CustomControl (so it is Restyleable, and usable in VS2012 Design Mode)
- Canvas Placement better support
- Resize/Move Controls when Zoomed
- Support of Editing Gradient Brushes after first Edit
- Preview in Propertygrid
- Highlight Selected line in PropertyGrid
- Support for Controls from Other Assemblys (Enter Correct namespace in Root XAML)
- GrayOutArea fixed (Befor it Grayed-Out not only the Edit Area...
- Raster Placement support
- Raster Placement and Snapline Placement can now be disabled/enabled via 2 Buttons in DesignSurface like in VS2012
- DragDrop over UserControls does not remove their Content any more!
- Clone (Copy) Objects in Outline View (XamlDesignItem now Cloneable!)