Add tests of cross-modulestore import/export

[LMS-2945]
Skip DraftVersioningModuleStore tests
Add the manual testing course for testing xml import/export across modulestores
Explicitly create the AssetKey for all assets coming out of a ContentStore
Don't use raw asserts in split (to handle different types of UsageKeys sanely)
Only compute block types with children once
Use field scopes to compute which metadata to strip from the definition during XML import of XMLModule subclasses
fix shib reg from course about page
Merge pull request #4445 from cpennington/cross-store-xml-import-export

Add tests for xml import/export between different modulestores
removing thread-local cache for branch_setting
recommender prototype
make sure the CourseAccessRole Django ORM Admin page uses a raw_id so that we don't populate millions of rows from the production database in the drop down list
Merge pull request #4303 from edx/danielli/recommender_prototype

recommender prototype
Merge pull request #4464 from edx/jbau/remove-branch-setting-cache

removing thread-local cache for branch_setting
always include GA file
Merge pull request #4450 from Stanford-Online/jbau/edx/fix-shib-student-register

fix shib reg from course about page
Piecemeal conversion to draft needs to allow
already converted children.
STUD-1965
Merge pull request #4437 from Stanford-Online/giulio/theme-segment-io

always include GA file
Default ENABLE_ANALYTICS_ACTIVE_COUNT to False for dev envs
Merge pull request #4462 from edx/bug/delete_draft

Piecemeal conversion to draft needs to allow