Display room name along with menu bar.

Includes some refactoring to send URIs instead of strings along with the
intent to AppRTCDemoActivity. This un-breaks opening URLs opened from
other applications.

This fixes #11 (intentionally), incidentally fixes #9 and incidentally fixes #15.
I believe we loose a bit of the (not perfect) sanity checking for the URL that we used to have in URLUtil.isValidUrl.
Please bring back some, since it seems like Uri.parse returns non-null values even for invalid URLs.