Shared sim

thoughts about this?

this creates a static lib of rts/Sim/* which is used for spring & spring-headless: ~160 .cpp aren't compiled twice any more when building spring + spring-headless.

only (possible) troublesome change is in rts/System/Sound/* as some stuff is now dynamicly allocated, before it was static. rts/System/Sound still needs some cleanup i guess (make an interface for EFX for example), but atm everything seems to work as before, this is why i want to merge it.