Add transcriptions_sources_count to element lists filters

See merge request !706

Add region source to both classifications and elements

See merge request !696

The regions migration was done before the addition of
sources on elements, but due to the order in which they
have been merged, sources were added before it.

To avoid re-running the documents.0009 migration, one can
use the following SQL query, assuming nobody has yet created
new elements with the new types created from regions:
UPDATE documents_element elt SET elt.source_id = cls.source_id
FROM documents_classification cls
WHERE elt.id = cls.element_id
AND elt.type_id IN (SELECT id from documents_elementtype WHERE slug LIKE 'region_%');

Fix GitLab OAuth callback errors

See merge request !704

Update image defaults for CI builds

See merge request !703

Ensure full Unicode support on bulk transcription endpoints

See merge request !702

Remove model Event and enum EventType

See merge request !705

Make text and zone required on transcriptions

See merge request !697

Handle possible path updates when checking an image in CreateIIIFImage

See merge request !700

Remove unused extract_transcriptions method

See merge request !701

Prevent children from interfering with their parents' neighbors

See merge request !699

Children are annoying.

Fix migration linting

See merge request !698

Move MLClass APIs to documents.api.ml

See merge request !668

Remove the vendors-main CSS from the CDN view

See merge request !695

Remove Himanis-specific stats from manage.py telegraf

See merge request !694

Remove regions

See merge request !687

Upload backend static files to /static

See merge request !693

Add django-redis-cache support

See merge request !692