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/GameRules/WeaponInfo.cs

@@ -131,7 +131,7 @@ namespace OpenRA.GameRules
 		public readonly List<IWarhead> Warheads = new List<IWarhead>();
 
 		/// <summary>
-		/// This constructor is used solely for documentation generation!
+		/// This constructor is used solely for documentation generation.
 		/// </summary>
 		public WeaponInfo() { }