Change notification scheme

[jamespizzurro]

As of now, we're using the browser's default notification scheme to alert users about crossing virtual picket lines. This works well enough, but the experience isn't consistent between platforms (e.g. Windows, Mac, Linux) nor browsers (e.g. Chrome, Firefox, etc.), and that's not ideal; while users should be familiar with the way their platform and browser handles notifications, a given notification scheme for one of these platforms and browsers might not be the best way to alert users that they're about to cross a virtual picket line.