Refactor WebAgg so it's easier to embed in other applications and run
over a server other than tornado.
Make figure larger.  Print address to console.
Let the Javascript side control when to fetch new frames.  draw_idle
sends a "draw" message to the browser.  If the browser is not already
waiting on another frame, it sends a "draw" message back to the server
which then returns an actual frame.  The nice thing about this approach
is that it's completely timerless.
Merge pull request #2420 from mdboom/webagg-factor

Refactor WebAgg so it can communicate over another web server