Upgrade Wagtail Content Vectors API to Wagtail > 4.x compatibility, bring to feature parity with Wagtail Images

Required by #4 in order to update Acorn website template to Django/Wagtail 4.x.

• Upgrade choosers and other application components to Wagtail 4.x API structure
• Update frontend components to follow new patterns and utilize base views
• Add multi-vector uploader application with support for drag/drop, tagging, and editing of upload attributes
• Add support for filtering by tag within the modal window (a96a6e99)
• Add support for bulk actions: delete, tag, add to collection (4ad3142f)

OP#38