change magic first line of behavior js files to a commented-out json blob, which should include the fields 'url_regex' and 'request_idle_timeout_sec'; behavior.is_finished() incorporates the custom idle timeout into its check; also rename variables in behavior scripts with umbra/UMBRA_ prefix to sort of namespace them; and add "finished" logic to facebook and vimeo behaviors (flickr needs work to support it)
UmbraWorker.send_to_chrome() - central place to send message to chrome via websocket