Use PlainText lexer from Rouge

I got a NameError for the Text lexer, and digging into the rouge
codebase, it looks like this is the fix for it.

I opened a ticket to verify:

https://github.com/jayferd/rouge/issues/92
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.
Merge pull request #700 from barrettclark/issue284_mentions

Add the notion of a mention.
Add redirects from the old dashboard
Fix dashboard links.
Fix nitpick navigation
Merge pull request #702 from Gaelan/patch-1

Fix dashboard links.
updating bob test error code help test to be more accurate
Merge pull request #703 from koriroys/kjr/ruby-bob-test

updating bob test error code help test to be more accurate
haskell robot-simulator cleanup (tests imported untested API surface)
Merge pull request #705 from etrepum/haskell-robot-fix

haskell robot-simulator cleanup (tests imported untested API surface)
rewrite simple-linked-list README
ruby simple-linked-list
haskell simple-linked-list
fix simple-linked-list.md formatting