Add rubocop to enforce style rules
Adding two rake tasks

* Rename cane.rake in lib/tasks to quality.rake (and the namespace)
* Add a rake task there for rubocop as specified in their wiki
* In travis.yml run both rubocop and cane with the rake quality:all task
Merge pull request #655 from RapidRailsGirls/remove_tabs

Added Rubocop configuration