Fix and enforce code style in Mods.Common, D2k, and TS.

It flags cases like https://github.com/OpenRA/OpenRA/blob/bleed/OpenRA.Mods.Common/Widgets/Logic/SettingsLogic.cs#L354 as an error.  Removing those empty lines hurts readability there, and I don't recall seeing style issues in our code that this would catch.

http://stylecopplus.codeplex.com/ specifically calls this out, and provides a modified version that behaves better.