Rotation axis update

Addresses #82. The changes I made are actually not domain-specific and there was a lot of them, so to make sure everything is OK I am making a PR. The biggest changes:
* rotation axis measure is now a function not a class
* rotation axis aligner is now a function not a class
* image processing routines moved to the proper module

You don't have to spent much time on it, it's here just for case I missed something.