More Mods.RA/Mods.Common reorganisation

Moved a couple more traits and activities to Common, moved a couple of ra-specific traits into the new namespace/folder structure.
Actually, after taking a closer look, this one is a bit tricky.

The problem is that the base ```Activity``` is not located in its own namespace/folder, but rather in ```Traits```.
Of course I could simply move ```CallFunc``` there, too, but if we want to do this properly and keep things consistent, we'd have to move the base ```Activity``` and ```CallFunc``` into a separate ```OpenRA.Activities``` namespace.