hack around Persona "no-resource://" limitation with a local http server
don't serve the .png through the local server, we can't handle binary
oops, empty strings are still true
store control-panel files on an external host, instead of using resource://

This is unfortunate, and expands the reliance set considerably, but the
local-http server wasn't working very well. Eventually we need to add
a Persona jetpack module with a native UI.
we get firebase.js from the CDN for now, not a local copy