Rename template for clarity
Don't clobber existing test suite
Rename Dashbord to Nitpick

The Dashboard should be the user's personal dashboard, not the pending
list of submissions to nitpick. By the same token, the presenter is now
called a `workload`.
Refactor User#ongoing
Create a very basic dashboard

Add suggestion to nitpick a particular user. See #173.
Add the notion of a mention.

- Look through the comment to find @username
- Add the mention list at the end of the nitpick with links to the exercism profile
- Add that to the list of submission participants
  - that taps into the existing notification system
  - exploit the fact that no guard exists to keep someone out of a submission given the correct submission ID
- Tested all the things that I could find. I couldn't figure out how to test sending emails. I didn't see emails sent for any nits.