Suggestion: Push notifications only on a single device

Currently, Keybase sends a notification in all the devices connected to an account. Alternatively, there could be an option to send only to the currently active device, where the fallback would be to send to a mobile device (similar to how it's done with some other clients).

With that option enabled in my settings, as a laptop user, I will receive the notification on my laptop when active on it, and when inactive, notifications would be received on my mobile device connected to Keybase.

This would resolve the current weird situation where I sit on my laptop and both devices get notified at the same time unnecessarily.

No files, tests, or entry points are named. Start by locating the notification delivery and device-activity handling in the Keybase client, then define how an active laptop should be selected and how mobile fallback behaves; done means notifications are routed to one appropriate device instead of all connected devices.

Written by the indexing model from the issue text.