Add config GUI to control notifications from experiments

[aaaaalbert]

In the usual "donating resources" use case, we will not want the experiment being able to output any notifications to the user (no sound, no text-to-speach, no alert boxes on the screen, no vibration). However, if you are doing things with your own phone while developing code, I think this would come in handy because it shortens the development and debug cycle.

(In the future, donors may be interested in running specific experiments that are designed to give them feedback. Who knows.)

For this, the app should respect any current media volume / "mute" settings (which it probably does out of the box), and likely provide a "do not disturb" or similar config item in the GUI that disables notifications from experiments temporarily.