implement Ordos nerve gas missiles as warheads

closes #2838
Merge pull request #6679 from Mailaender/change-owner-warhead

Implemented Deviator nerve gas missiles as warheads
Move more traits from Mods.RA to Mods.Common
Rename Util.cs to BuildingUtils.cs
Move Activities CallFunc, RemoveSelf and SimpleTeleport to Common
Move various RA-specific traits to the new folder/namespace structure
Move 'Activity' into its own namespace in OpenRA.Game.