Session's view list RefItems should not require a database to be specified

The view list RefItems will eventually be removed entirely in favor of
direct references to views.
Remove all use of "img" and "db" fields in views, in favor of ViewerRecords
Fix favorite creation to save fields appropriately as ObjectIds
Rename use of 'image_image_store' to 'image_store'
Remove unused Python imports
Merge branch 'view_schema_cleanup'

* view_schema_cleanup:
  Remove unused Python imports
  Rename use of 'image_image_store' to 'image_store'
  Fix favorite creation to save fields appropriately as ObjectIds
  Remove all use of "img" and "db" fields in views, in favor of ViewerRecords
  Session's view list RefItems should not require a database to be specified