Content libraries UI updates

- On the dashboard page, the blue border now appears only when the state is active. On hover for an inactive link the text color gets changed to black, but the bar is not shown.
- Update the copy of the text on the new library form to match the design and removed the beta warning on top of the form.
- Remove ability to edit the name of the library container on the top left of a library page and make `display_name` library field non-editable.


@mtyaka Sounds good, thanks!

@e-kolpakov Cf above - do you know why the "Edit" doesn't show on the sandbox based on https://github.com/edx/edx-platform/pull/6046 ?