Whitespace and import cleanup

I wanted to contribute but did some clean up first, with the intention of conforming to [PEP 8](http://www.python.org/dev/peps/pep-0008/) which will encourage others to contribute

These changes are all automated making it very unlikely that it broke anything, and tests still pass. You can read the commits for more detail on the types of changes included. Most notably, I replaced all tabs with 4-spaces as is the standard. (Most text editors allow you to change your default.)

I can PR the following after this is accepted (below are links to "as-if" pull requests; i.e. PR's to my personal fork):
- https://github.com/dannyroberts/imbox/pull/1
- https://github.com/dannyroberts/imbox/pull/2