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/Map/MapPreview.cs

@@ -63,7 +63,7 @@ namespace OpenRA
 
 	public class MapPreview : IDisposable, IReadOnlyFileSystem
 	{
-		/// <summary>Wrapper that enables map data to be replaced in an atomic fashion</summary>
+		/// <summary>Wrapper that enables map data to be replaced in an atomic fashion.</summary>
 		class InnerData
 		{
 			public int MapFormat;