Update the README of the CMS's CourseGraph support app:
* Point to the newly-developed CourseGraph plugin for Tutor,
and remove some prose that's now redundant with the Tutor
plugin's README.
* Add a link to the now-public CourseGraph Queries wiki page.
* Capitalize the G in CourseGraph.
* Fix a couple misc. formatting things.
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.
