Made Common namespaces more consistent

This is a follow-up on the decision we've come to in #7036.

A lot of the traits in Common still used old RA-style namespaces. This moves them to Common.Traits.

Additionally, this moves a couple more traits from RA to Common.
I was thinking the same thing. Don't know how popular it will be, but it is the clearest solution.
Until then I'd still rather have `using RallyPointTrait = OpenRA.Mods.Common.Traits.RallyPoint;` here though.