WP DrawingSurface & Resume

Notes:
* added support for rendering to DrawingSurface (http://monogame.codeplex.com/discussions/435425, http://monogame.codeplex.com/discussions/432138, http://monogame.codeplex.com/discussions/403764)
* fixed problem with Game.Dispose and than recreating Game object (http://monogame.codeplex.com/discussions/435932)
* fixed resume on Windows Phone (#1471)

When adding support for rendering to DrawingSurface, a new parameter was introduced to XamlGame.Create:

static public T Create(string launchParameters, PhoneApplicationPage page, UIElement drawingSurface = null)

Default value is added so any existing code will work as it did before; however one can manually specify on which surface to draw, currently drawing surface can be either DrawingSurfaceBackgroundGrid or DrawingSurface. Please feel free to comment/change this change to XamlGame.Create. This is the only public API change, other stuff is internal. One can use same approach as for MediaElement, that is to search for DrawingSurfaceBackgroundGrid or DrawingSurface within UI tree and ditch the third parameter from Create.

EDIT:
Due Nezz@6ed2156 we eliminated the third parameter from Create so Create method stays the same.