Websockets merge unstable

[rtibbles]

Summary

Description of the change(s) you made

Merge mostly straight forward.

# Conflicts:
#	Makefile
#	contentcuration/contentcuration/frontend/shared/data/applyRemoteChanges.js
#	contentcuration/contentcuration/frontend/shared/data/resources.js
#	contentcuration/contentcuration/frontend/shared/data/serverSync.js
#	contentcuration/contentcuration/settings.py
#	contentcuration/contentcuration/viewsets/base.py
#	contentcuration/contentcuration/viewsets/channel.py
#	contentcuration/contentcuration/viewsets/sync/endpoint.py
#	requirements-dev.txt
#	requirements.in
#	requirements.txt

Main complexity was in serverSync.js where I opted to conditionalize the syncChanges and debouceSyncChanges functions to do the websocket send or normal endpoint poll. This seemed like the simplest way of adding in the new behaviour while retaining the mutliple changes that have happened in unstable.

Caveat: due to a bug with the reactive listening to changesRev.length this doesn't currently send any changes via websockets, so this won't work if you test manually.

Manual verification steps performed

1. Make an edit.
2. Refresh the page to make sure the sync gets sent.
3. confirm that the changes get propagated to another browser session by the websockets

Does this introduce any tech-debt items?

Still need to work out a way to properly trigger the websocket send.

References

Fixes #4159

Comments

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Contributor's Checklist

PR process:

• If this is an important user-facing change, PR or related issue the CHANGELOG label been added to this PR. Note: items with this label will be added to the CHANGELOG at a later time
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Reviewer's Checklist

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• Automated test coverage is satisfactory
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• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
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