Review StyleCop rules.

- Enforce SA1604 ElementDocumentationShouldHaveSummary.
- Enforce SA1629 DocumentationTextShouldEndWithAPeriod.
- Turn off some rules covered by IDExxxx rules.
- Remaining rules are treated as part of OpenRA style.

OpenRA.Game/Graphics/Model.cs

@@ -26,7 +26,7 @@ namespace OpenRA.Graphics
 		float[] Bounds(uint frame);
 		ModelRenderData RenderData(uint section);
 
-		/// <summary>Returns the smallest rectangle that covers all rotations of all frames in a model</summary>
+		/// <summary>Returns the smallest rectangle that covers all rotations of all frames in a model.</summary>
 		Rectangle AggregateBounds { get; }
 	}