Make email notifications configurable

:convenience_store: 

There are 3 different emails that go out regarding cookbooks:
* New version of a cookbook
* Cookbook deleted
* Cookbook deprecated

Previously, all of those emails were handled through 1 boolean column.  Now each of those 3 is exposed as its own preference on the profile management screen.  Additionally, all of those emails now contain unsubscribe links.

Closes https://github.com/opscode/supermarket/issues/814