In-line Analytics

PR for internal review purposes as prelude for PR to upstream
    PR'd against copy of upstream master.

Known issues to be fixed later:
- Styling is embedded in html file as prelude to re-styling
- No tests
- pep8 and pylint not looked at yet.

@jbau @jrbl @stvstnfrd @caesar2164 if you please.
I would put this code in `common/lib/capa`.  You're getting all the choices for a multiple choice question.  This belongs there, if nothing else for modularity and maintenance.