devilry_header: Search UI skeleton.
devilry_header: Search UI usable but ugly admin content search (#308).
apps.core.search_indexes: Search index for AssignmentGroup (#308).
apps.core.models.assignment_group: Tests for get_all_admin_ids.
apps.core.search_indexes: Include students and examiners (#308).
apps.core.models.devilryuserprofile: Added get_displayname.
apps.core.models.devilryuserprofile: Fixed get_displayname.
devilry_search: Various improvements to search results (#308).
apps.core.search_indexes: Do not include tags and examiners in text (#308).

This data should only be available to admins, so we use separate fields for them (examiners are included in text on non-anonymous).
apps.core.search_indexes: Correct templatenames.