Moving generic RTS code from OpenRA.Mods.RA to OpenRA.Mods.Common

- Moved a sizeable chunk of the Traits, Activities and Orders from the RA mod project to Common
- Fixed classes in OpenRA.Mods.D2k project being declared in namespace OpenRA.Mods.RA
- Dune 2000 and Tiberian Sun mods no longer have ANY dependencies on OpenRA.Mods.RA
- Restructured refinery-related code

Yes, it is a big commit, but it should get the job done. Anything that is left to be moved should be transferable with simple editions to the using statements and the namespace.