app should be able to receive comments from graders on short-answer questions

[usernamenumber]

comments can be generated by a webapp that queries the lrs, but we need a way to get them back into the app, associated with the question, and displayed to the user somehow.

See also #110

[usernamenumber]

Assuming comments are stored in the LRS and associated with answers using some sort of key the app can recognize, learninglocker's aggregate API call should do what we need.

[usernamenumber]

More implementation notes after the last meeting:

• We'll need something in the app to periodically check for an Internet connection and pull down any pending comments
  • (@Jakeii): This can be accomplished with a service worker
• (@limikael): Comments can be stored in such a way that they can be grouped with a question and then retrieved with a query like http://xapi_endpoint/statements?activity=http://questions.tunapanda.org/user@email/the_question_id&related_statements=true
  • The key thing here is related_statements=true. See here for the relevant API docs.
• The app will need to be able to store locally...
  • Comments associated with questions+users
  • Set up an ember model with relations to User (we don't have a model for content down to the question level), and populate it with the permalink of the relevant question as each comment is received
    • This assumes the permalink for the question is in the xAPI for the answer+comment; I think it is, but that should be checked in the LRS or code to be sure.
  • The timestamp of the last (successful!) check, so we can use the aggregate api (linked above) to only grab statements since the last check.
• The original spec from Certel is only for allowing teachers to comment. Though two-way communication should be possible, we will start with one-way.