Kontrast Cleanup

Work In Progress!

Since this is now being used internally, I don't want to commit to master anymore.
This pull request is to prepare Kontrast for public release.

Feature todo:
- [ ] Config file generator
- [x] Rails detection
- [x] Move non-zero diffs to the top of the gallery (well, I added a nice link section)
- [x] Sort the rest of the gallery into a more meaningful order
- [x] Parallelize selenium and image handling via workers
- [x] Figure out how to make remote integration and uploading nicer
- [x] More tests

Administrative todo:
- [x] Update README
- [x] Confirm license
- [ ] Write blog post
- [ ] Publish gem
Can't you just do `if Rails? && [3,4].include?(Rails::VERSION::MAJOR)`