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/WAngle.cs

@@ -102,7 +102,7 @@ namespace OpenRA
 
 		/// <summary>
 		/// Find the index of CosineTable that has the value closest to the given value.
-		/// The first or last index will be returned for values above or below the valid range
+		/// The first or last index will be returned for values above or below the valid range.
 		/// </summary>
 		static int ClosestCosineIndex(int value)
 		{