Update Note with renames and API category

- Split out the API usage into a category for organization

- Rename confusing ‘sync’ method to `mergeNewNotes:` like other models
Method name change

- checkNotifications -> fetchRecentNotifications; fetches the last 20
Add refresh single note to Note

- Remove redundant getter, use property getter instead
Use Note to keep API calls organized

- While not ideal, it gives more meaning to the API calls

- Most Notes related calls sync the notes after the response comes back, so keep this in Note

- Remove redundant ‘user’ reference in controller that points to WordPressComApi