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.
Merge pull request #7129 from reaperrr/ra-common15

More Mods.RA/Mods.Common reorganisation