Implement Pagination for Content libraries (SOL-4)

* **Background**: This PR provides pagination for content Libraries in the container view, when displaying the blocks contained in the library.
* **Jira tickets**: Implements SOL-4
* **Discussions**: Architecture discussed extensively on the wiki and in meetings, then the revised proposal was presented to the Arch Council on Oct. 21 and given thumbs up.
* **Dependencies**: https://github.com/edx/edx-platform/pull/6046 (merged, in feature branch https://github.com/edx/edx-platform/commits/content-libraries)
* **Sandbox URL**: http://sandbox.opencraft.com:18010/library/library-v1:TST-X-01+now
* **Internal code reviews PRs**: https://github.com/open-craft/edx-platform/pull/9 https://github.com/open-craft/edx-platform/pull/18
* **Partner information**: 3rd party-hosted open edX instance, for an edX solutions client.

Note that we did something similar on the original container page so that we just updated in place. However, that was easier as we didn't have to bring in additional paged content.