Remove DimensionalityError 

We haven't been 100% consistent in using `DimensionalityError` in Menpo. We certainly never rely on it for catching errors, and with it not being used consistently it's not terribly useful.

This PR replaces all occurrences of `DimensionalityError` with `ValueError` (it's superclass). In the future we may wish to revisit adding Exceptions to Menpo but for now simplicity of sticking with builtin errors trumps verbosity.