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.

This will allow the InvalidKeyError to escape if course_id is malformed. Change to the following:

```
course = None
try:
    course_key = CourseKey.from_string(course_id)
    course = modulestore().get_course(course_key, depth=None)
except InvalidKeyError:
    pass

if not course:
```

Sorry to cause more churn; I should have read the previous suggestion more carefully.