Refactoring includes

Use of request.user instead of passing user_id in every HTTP request
Updating of the view only after successful API response
Renamed status of each item from finished to checked
Use of ChecklistItem non-database resource API instead of using HTTP request parameters
Moving of front-end API logic from view to model
CSS hyphens everywhere instead of underscores
Improving Python code (renaming variables, removing redundant code)
Start checklist item IDs from 0 instead of 1.

Basic CRUD functionality remains. Ensured that the views will not update unless there is a successful response from the server.