Add an endpoint for syncing a user's course status metadata

JIRA: MA-75

proposed path: users/{user}/course_status_info/{course_id}


Some things I am looking for feedback on:
1. Name of the endpoint. I've been calling it course_status_info but maybe metadata is a better word?
2.
  - Arguments. Name: last_visited_module_id.
  - Format: Right now I have it as form encoded on the setter. Should the body be JSON?

Also adds an "id" field to the path returned as part of the video_outline.

@gwprice @nasthagiri 
Note that this does not include combining the getter here with the video_outline endpoint into a new endpoint as we discussed. I figured we needed to have the symmetric getter for the setter no matter what and that would unblock Clarice. I'm happy to combine those into a new endpoint if we still think it's a good idea.

There are parts of the code in courseware/views I was working with that make that assumption, so I figured it was okay. But also, looking again, they actually define that constant in that file (while also mentioning a bare '2' a bunch of times) and I totally missed it, so it's definitely redundant here. I'm happy to just recurse as far as it goes.