[SPACES] Ability to submit (students) and read (teachers) responses to reflection questions

AC:
- [ ] should save answers to activity entry to separate content-type called **responses**
- [ ] **responses** content-type should hold reference ID to **activity** content-type and user ID

Start by locating the activity content type and the code that saves activity entries, then trace how teachers currently read activity data. Add the responses content type with activity and user references, save student answers there, and verify that teachers can read them for the related activity.

Written by the indexing model from the issue text.