The `get_course_last_published` function is used by CourseGraph to
determine whether or not a course should be dumped to Neo4j.
If the course hasn't been published since it was last dumped to
Neo4j, then it can be skipped (unless the override_cache option
is enabled).
The function was previously built using the BlockStructure
data model. While this worked fine in Production instances that
enable `block_structure.storage_backing_for_cache`, this
implementation did NOT work in development environments,
which do not use the BlockStrcture model.
Instead, we switch to using CourseOverview.modified to
approximate when a course was last published. This is method
has fewer moving parts and is universally available across
instances.
Introduce a new CMS settings COURSEGRAPH_CONNECTION,
which allows operators to specify default connection paramters
for a Neo4j instance.
This has three purposes:
* The `./manage.py cms dump_to_neo4j` management command will be
much easier for developers and operators to type out because connection
arguments can now be omitted. Note that connection arguments, if
supplied, will override the arguments specified in CMS settings.
* The automatic push-to-coursegraph-on-publish-signal introduced in
subsequent commits can use these connection settings.
* The CourseGraph Django admin actions introduced in subsequent
commits can use these connection settings.
This code was originally located at:
./openedx/core/djangoapps/coursegraph
However, code makes more sense within the ./cms tree, because:
* it is responsible for publishing course content to an
external system, with is within the responsibilities of CMS, and
* is uses modulestore, which is discouraged for use in LMS
(see 0011-limit-modulestore-use-in-lms.rst).
So, we move the code to:
./cms/djangoapps/coursegraph
and uninstall coursegraph from LMS.
We do not expect this refactor to have any breaking downstream effects.
