[LMS-226]
[LMS-2013]

Added sorting to the new pagination logic for STUD-995.

STUD-1072

Updated the pagination tests to no longer use the toy course, but to instead explicitly upload the assets it needs.

 Added a new AssetsTestCase base class to own shared helper methods.

STUD-878

These changes implement STUD-813. The commit consists of the
following logical changes:
 - a REST API has been implemented for a course's assets
 - the page itself now fetches the assets client-side
 - the Backbone.Paginator library is used to support pagination
 - the AssetCollection has been refactored to extend
   Backbone.Paginator.requestPager so that it can be paged
 - an abstract PagingView class has been added to generalize
   the communication with a paging REST API
 - the AssetsView has been reimplemented to extend PagingView
 - two new child views have been added:
   - PagingHeader: the paging controls above the list of assets
   - PagingFooter: the paging controls below the assets

on new Locators to make it clear that they have a different syntax
than Location.course_id altho they represent the same info.

[LMS-1614]

and fix found errors.

usage_id implies self-sufficiency. The block_id is relative to its structure.

STUD-1048

STUD-1030

LMS-1551

STUD-945

Part of STUD-870

Ensure user admin screen gets the union of all possibly matching group names.
Smarter default group naming.
STUD-1003

Part of STUD-870

STUD-948

"as_published" changes I previously put in, as now we
are not adding @draft to locations converted from locators.

STUD-844

STUD-946
STUD-947

STUD-850

STUD-849

STUD-941

STUD-848

The draft.py solution only worked when the parent was also in the draft store.

Reviewed and updated all on-page panel help text in Studio for clarity,
consistency, and brevity.  Updated template HTML files to change text

STUD-924

Part of STUD-847.

html page and update access use 2 different urls
GET update can get an individual update
STUD-944

Part of STUD-847.