[Toolkit.Graphics] Added OcclusionQuery

Based on XNA's OcclusionQuery (http://msdn.microsoft.com/en-ca/library/microsoft.xna.framework.graphics.occlusionquery.aspx).

On instantiation, determines whether or not the graphics device supports queries with the occlusion flag as well as support for minimum feature level (> 9_1).

I can provide a simple sample based on how I use this in my engine code, but since SharpDX samples solution uses nuget, I'll merge it if the PR actually makes it that far.