Add File, LocalFile, ContentTag, and AssessmentMetadata models to kolibri_public

[bjester]

Parent: #3808
Depends: #3927

Desired behavior

• Add a new model ContentTag to the kolibri_public app
  • Could inherit ContentTag from Studio's kolibri_content
  • It should have fields id and tag_name
• Add a new model LocalFile to the kolibri_public app
  • Could inherit LocalFile from Studio's kolibri_content
  • It should have fields id, extension, and file_size
• Add a new model File to the kolibri_public app
  • Could inherit File from Studio's kolibri_content
  • It should at least have fields: id, contentnode_id, preset, lang_id, local_file_id, supplementary, and priority
  • The lang field (lang_id) should be a FK to the core Language model
  • The local_file field (local_file_id) should be a FK to the LocalFile model
• Add a new model AssessmentMetadata to the kolibri_public app
  • Could inherit AssessmentMetadata from Studio's kolibri_content
  • It should have fields: id, contentnode_id, assessment_item_ids, number_of_assessments, mastery_model, randomize, and is_manipulable

Current behavior

The models do not exist

References

• ContentTag Kolibri model / ContentTag Studio model
• LocalFile Kolibri model / LocalFile Studio model
• File Kolibri model / File Studio model
• AssessmentMetadata Kolibri model / AssessmentMetadata Studio model

Value add

These models will support remote content browsing on Studio

[rtibbles]

Fixed in #3955