Better thrusters

Adds directional fade and quads along the axis to make it look nice from all angles.

Its still a bit skanky in that some models have their thrusters inside the model, and the axis quads can leak out (Wave is a particular good example). But I think I can live with that in exchange for big bright thrusters that can obviously burn your face off from all sides :)

![](http://i.imgur.com/SNlfBBI.png)

![](http://i.imgur.com/6gKSUoI.png)

![](http://i.imgur.com/WHtZBtw.png)

Closes #1960.