Get console logs, fail when error logged

[noahgibbs]

Chrome allows just grabbing error logs that have already occurred: https://stackoverflow.com/questions/46278514/capture-browser-console-logs-with-capybara

That's workable. It would also be possible to replace the console.log/console.error etc functions with something that captures them. But it's nice to be able to grab error logs natively because that works with browser stuff that goes around the JS definitions and also works when Scarpe fails to boot properly, so it may not be able to replace the console.log, console.error, etc functions.

[noahgibbs]

Partway there. We can grab error logs now, but we don't yet error on them.