Moved RenderSprites.cs from Mods.RA to Common

Moved file RenderSprites.cs.
Moved interface IRenderActorPreviewInfo  from OpenRA.Mods.RA/TraitsInterfaces.cs  to  OpenRA.Mods.Common/CommonTraitsInterfaces.cs.
Naturally, a lot of "using"s needed to be added.

Note: I intentionally left a ton of unused "using" statements to reduce the number of differences and facilitate reviewing. I will do a clean-up for these at some point. (when more files are moved perhaps).