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/RgbaColorRenderer.cs

@@ -78,7 +78,7 @@ namespace OpenRA.Graphics
 		/// <summary>
 		/// Calculate the 2D intersection of two lines.
 		/// Will behave badly if the lines are parallel.
-		/// Z position is the average of a and b (ignores actual intersection point if it exists)
+		/// Z position is the average of a and b (ignores actual intersection point if it exists).
 		/// </summary>
 		float3 IntersectionOf(in float3 a, in float3 da, in float3 b, in float3 db)
 		{