BOM-630

python3 compatibility

BOM-484

BOM-432

REST API docs

Disable edxnotes for blockstore runtime.

Blockstore runtime does not support courses currently and it will
not have the modulestore attribute in any case.

This commit introduces the changes needed for XBlocks in Blockstore to save
their user state into CSM. Before this commit, all student state for Blockstore
blocks was ephemeral (in-process dict store).

Notes:

* The main risk factor of this PR is that it adds non-course keys to the
  course_id field in CSM. If any code (like analytics?) reads course keys
  directly out of CSM and doesn't have graceful handling for key types it
  doesn't recognize, it could cause an issue. With the included changes to
  opaque-keys, calling CourseKey.from_string(...) on these values will raise
  InvalidKeyError since they're not CourseKeys. (But calling
  LearningContextKey.from_string(...) will work for both course and library
  keys.)
* This commit introduces a slight regression for the Studio view of XBlocks in
  Blockstore content libraries: their state is now lost from request to request.
  I have a follow up PR to give them a proper studio-appropriate state store,
  but I want to review it separately so it doesn't hold up this PR and we can
  test this PR on its own.

minor fixes

minor changes

BOM-485

BOM-483

Feanil/unpin pip tools

python3 compatibility

Adds config model to pass arguments to management command

BOM-486

This would enable simulate_publish management command to
fetch its arguments from config model.

PROD-548

API docs are now always available, no more toggle to enable them.

Show Upgrade Deadline in Studio

This shows the verified upgrade deadline for the course, as a
read-only field.

DISCO-1345

BOM-422

Awais786/prod 692

BOM-438

SE-1553 conditionally run migration on CSMH Extended table

clean up toggle annotations and lint when running feature toggle report

Issue 851 seems to have been resolved and issue 8.5.2 while still open is
not occuring with the latest version of pip-tools.

Update edx-platform dependencies.

Fixing python3