Vector Thruster client optimizing

Over 4 years ago, someone optimized the thruster's effects, limiting it to just 1 shared ParticleEmitter, instead of a new one every client frame, which fixed a bug where source wouldn't create any more ParticleEmitters.
This, among other fixes, never got into vthrusters, causing them to occasionally break all particle emitters (with console spam) and overall have much worse FPS.

Now both VThrusters and Thrusters pull the same effects from wire/client/thrusterlib.lua, and now **Vector Thrusters no longer kill FPS!**

VThrusters: Effects now originate from the end of the model (like thrusters) instead of the middle

This is in preparation for #353

This needs to be tested, to make sure VThrusters still apply the same amount of force in all 3 modes (particularly concerned about the odd "XY Local Z World" mode). I have, but I need another confirmation.