Extended browser page watching times

[ato]

@ibnesayeed suggested that for certain types of content it would be useful to be able to keep the page loaded in the headless browser for extended periods of time (e.g. 15 minutes) in order to capture updates. Use cases might include chat systems, sports score trackers, image carousels, realtime notifications, audio-visual presentations (slideshows, demoscene and whatever the html+js equivalent of ye olde flash animations is called).