Display versions count on cookbook show.

This should give the user a better indication that there have been X released
versions and let the know that they can select the dropdown to view a different
version.

This should wrap up https://trello.com/c/4jhWRvuG

Looks like:

![screenshot from 2014-04-07 09 08 08](https://cloud.githubusercontent.com/assets/928367/2631189/ae594f3c-be55-11e3-95dd-b1bb79e56e5d.png)

@danvolkens that screenshot looks not polished and not aligned because I just tossed the element in there. Would you prefer that I tighten it up with some sort of class that adjusts the size or would you want to?