Implement Pagination for Content libraries

Jira Issue: SOL-4

Provides pagination for content Libraries in the Studio Editing View.

* Partner information: 3rd party-hosted open edX instance, for an edX solutions client (so will need to get some sort of solution merged in)
* Merge Deadline: Next Week, 11th of December
If I understand right, the [idea](http://bok-choy.readthedocs.org/en/latest/guidelines.html#put-browser-interactions-in-the-page-object-not-the-test) is to not have any css selectors in tests, but move them to page objects, so that tests are decoupled of markup.