Adds support for raycasting with morphs

This isn't insanely fast, but it stops the bug described [here](https://stackoverflow.com/q/13723473/102441), where the RayCaster assumes all meshes are in their unmorphed form.

Tested on a mesh with 10000 vertices, runs at a reasonable speed. The code path should only be taken if morphs are enabled anyway.

I've chosen time over memory here - it may be faster to precalculate all the morphed points, but then you end up allocating a lot of vector objects. Also, the calculations are written out elementwise to try and optimize for speed.