system: add panic mode to system settings

[s00se]

This feature adds a toggle to wipe notifications when the device enters airplane mode, stand-by mode, or starts charging

[jplexer]

Codewise this looks good to me, just want a final check by @ericmigi

[asyba]

From a privacy perspective, I understand that if the Pebble is lost, stolen, etc, the important information is the notification list.

One option is this one from PR, which involves adding the function to clear the notification list whenever Bluetooth can be disconnected.

Another option could simply be having a timer that clears the list every hour, for example, without having to depend on specific actions.

However, this approach has consequences. If I want to see a past notification, I'll find it was deleted because panic mode was activated, but it's an optional feature.

Perhaps having a system of deleting notifications every day or week would lessen the need to search for a past notification and the frustration of finding it deleted by this activated mode.

Since the Pebble doesn't have a password or PIN (perhaps with the touchscreen could be added with PTime2, but that might complicate things if we're looking for a simple watch).

I also recall that in another comment it was agreed that in some cases, when new options are added, they might be placed in a new menu called "Experimental," as if to say, "We don't know if it will be there permanently." but is here for now.

[ericmigi]

Interesting idea! Not something we'll merge right now, but as soon as we implement something in the mobile app that controls settings on the watch, we'll merge it and make it available as an advanced setting users can enable from the mobile app