Content libraries UI Updates (SOL-80)

* **Background**: This PR contains UI Updates for the content-libraries studio view and content block.
* **Jira tickets**: Implements SOL-80 and the reviews from https://github.com/open-craft/edx-platform/issues/23
* **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/6155
* **Sandbox URL**: LMS: http://sandbox.opencraft.com/ - Studio: http://sandbox.opencraft.com:18010/
* **Internal code reviews PRs**: https://github.com/open-craft/edx-platform/pull/19
* **Partner information**: 3rd party-hosted open edX instance, for an edX solutions client.
OK, I just looked at the sandbox, and I created a new account (to see what happens when no courses are associated to the user) and  - to me at least - I see what appears as sufficient messaging to the end user.