Review data returned by /courses/xxxx/info endpoint

[ssciolla]

Currently, all the data for the course model is included in the response to the GET api/v1/courses/xxxx/info endpoint. Because we use special logic captured by Course.determine_date_start and Course.determine_date_end (see #1431) to determine date ranges for the course, some of the data included in the /info/ response is not consistent or really needed at all (date_start, date_end, term?). We could benefit from an audit of that endpoint to make it streamlined.