Paging for LibraryView added with JS tests.
Added tests for Library pagination.
Addressed notes from reviewers on Library Pagination.
Factored out Pagination into its own Container view.
Addressed further review notes for Library Pagination
Merge pull request #6163 from open-craft/content_libraries/4-pagination

Implement Pagination for Content libraries (SOL-4)
Library Content XModule
Unit and integration tests of content libraries
LibraryContent bok choy acceptance tests
Friendly error message when library key is invalid
Added explanation to container view of Library Block.
Made errors on Library blocks use validate functionality.
Move update link to the validation area
Fix: don't need to reload the whole page to refresh_children from the container view
Refresh children automatically when library setting is changed
Fix greedy intrusion of split_test documentation
Validation should be on the descriptor, not the module
ungettext fix
Move code that uses the modulestore to an XBlock service
Display the library key on the library view in Studio