Create a Challenge Completed Activity

**I'm submitting a ...** (check one with "x")
- [ ] bug report
- [x] feature request
- [ ] support request => Please do not submit support requests here, instead ask your query in out Gitter channel ahttps://gitter.im/BashMug/HappyPanda

**Actual Behaviour**

There is no activity that shows up after the user completed the challenge.

**Expected Behaviour**

There should be an activity asking the user to take a photo and upload it on various social networking sites. This feature is optional.

**Steps to reproduce it**

> None

****Would you like to work on the issue?**

Yes

The issue names no files, tests, or entry points. Start by exploring the repository to locate challenge completion and activity handling, then determine how optional social-network photo sharing fits the existing design. Done means a completed challenge produces an optional activity prompting the user to take and upload a photo.

Written by the indexing model from the issue text.