Unit Test Improvements
TE-489
Implement course-wide asset paging methods.
Add SortedCollection class to help sort lists efficiently.
https://openedx.atlassian.net/browse/PLAT-74
Implement copy_all_asset_metadata for Old Mongo->Old Mongo.
Add tests for copying all asset metadata.
https://openedx.atlassian.net/browse/PLAT-74
Changes for PR review: More compact tests, enumeration for metadata
sort order, etc.
https://openedx.atlassian.net/browse/PLAT-74
Move all lms image files into lms/static/images [OPEN-303]
Merge pull request #5655 from edx/ammar/unit-improvements

Unit Test Improvements
Merge pull request #5819 from edx/jeskew/asset_mongo_coursewide

Implement course-wide asset paging methods.
Merge pull request #5822 from edx/sarina/OPEN-303

Move all lms image files into lms/static/images [OPEN-303]
Generalize assets to any block_type but using
AssetKey and the metadata store
PLAT-204