Option to stop mirroring notifications on idle devices

This is somewhat related to the suggestion to turn off mirroring when your phone is in use. Basically, the user should be able to turn off mirroring for devices which aren't being used. Put another way, only mirror notifications to devices which are being used.

Many people mirror notifications so they can monitor + respond to their phone while using a different device. As such, it's not too useful for notifications to accumulate on a device I'm not using at the time. When I'm actually using my PC, mirrored notifications are very useful—but it's *not* useful to open up my PC to a huge stack of notifications (which are already on my phone).

Now, I'm sure there are people who *do* like the current behavior, which is why I'm proposing a toggle.