Tools directory + supporting changes

:fork_and_knife: Alright here we go. This PR builds out the cookbooks index view and atom feed and refactors a bunch of stuff to support that feature. Here are the highlights. 

- Make the cookbook partial and simple cookbook partial styles more generic `listing` and `simple_listing` so they can be used for tools.
- Abstract the common UI element title with buttons into a class we can reuse throughout the application (and we are now).
- Remove a bit of dead SCSS.
- Limit tools so they can of the type `knife_plugin`, `ohai_plugin` or `chef_tool`.
- Add some tool seed data to work with in development.
- A few bug fixes
  - Seeds failed if you ran them twice, they don't anymore
  - Server side validations weren't working for the new tool form.
Not trying to be super nitpicky about this, but was this changed to owner to be more descriptive of what it is? I am fairly certain the app is rolling w/ Maintainer for the person who creates and manages Tools.