Clean up info div, and fix timer exhaustion error.

Previously, we would call setInterval on every updateInfoDiv update,
leading to T^2 timers being created, and the eventual death of the app.
Also clean up the layout of the info div.
Address CR comments.

Return undefined from extractStatXXXX
Report media RTT instead of STUN RTT
Merge pull request #39 from GoogleChrome/juberti-constraints4

Try #2: Clean up info div, and fix timer exhaustion error.