VERY dirty rendering

warning, rather hackey. do not merge.

not suitable for nearly anything except light hockey, as static objects never change anything without changing scale

ScaleComponent now contains an int _dirty, initialised at 10. Each render, 1 is subtracted from _dirty. Render is skipped if less than 0
changing scale sets _dirty to 1

Though it'd take a bit of a rethink to make this more general case, in Light Hockey the time taken by update@renders.pyx is nearly cut in half.