Add make_course_key to modulestores, so that external clients don't need to assume a CourseKey subtype.

Conflicts:
	common/lib/xmodule/xmodule/modulestore/xml_importer.py
Trying to get split to work
Import depth first to help w/ publishing
fixup - re-enable Asset checking.
Annotator Tools: Fix major logic bug in code
Move about overview creation to common superclass
Merge pull request #4754 from edx/diana/show-cert-without-end-date

Show Certificates Before End
Add Optimizely widget
Provide workarounds for skip_draft where other code doesn't want its behavior
Support xml blocks w/ multiple parents
Use new check counter & bump count
Support import of ErrorDescriptors.
Use continue version for create course side effects
Disable fetching by version guid for now
More branch override precedence refinement
Merge pull request #4760 from edx/oleg/turn-off-cdn-rc

Allow turning off Video CDN in Studio.
Merge pull request #4764 from edx/diana/show-cert-without-end-date

Show Certificates Before End
Merge pull request #3894 from mtyaka/patch-3

Update xblock-mentoring.
Merge pull request #4763 from edx/lms/add-optimizely

Lms/add optimizely
Merge pull request #4762 from edx/annotations-js-fix

Annotator Tools: Fix major logic bug in code (RC)