Adds integration specs for locked / unlocking features

Cool idea, guys.  I took the time to add integration specs with Capybara and tweaked a couple of related things:

* Added HTML entities to the `unlock.html.erb` view (I was getting weird character encoding issues in my specs when these were just bare UTF-8 characters)
* Used `ActiveSupport::Concern` to make the inclusion of the Lockup `before_filter` more idiomatic.

Let me know what you think.