remove multivariate_normal hack, mayavi standard dep, gitignore

Continuum have just added SciPy 0.14 to conda's repository, so we have no real need to keep our nasty hack for `multivariate_normal` any more (see #304).

I've also moved mayavi to be a standard dependency (since it really is for the time being, and certainly for 0.3) and added a miscellaneous IntellIJ file to the `.gitignore`.