Implement SharedWorker-based updater (almost)

Oh, the things that I do to make this work in Greasemonkey ;_;.
I really should just jump ship to a proper extension, everything
would be less hacky.
Implement SharedWorker-based updater (working)

It works! I left all my debugging printlns in so
others can see my shame. I swear I'd use the actual
debugger if I could.