Turn off "Other" notifications by default in Juno

[cassidyjames]

We want to encourage apps to use the notifications API properly with the freedesktop ID and everything. In Loki, we grouped all non-compliant apps together under "Other" in the Notifications plug. In Juno, I think we should turn those notifications off by default.

This means that out of the box:

1. Apps using the API properly work as expected.
2. Apps not using the API properly can update to use the API properly to get notifications back on by default.
3. Apps not using the API that don't update can still be opted into by the user by switching on "Other"

[danirabbit]

Something kind of annoying that I noticed about this is that some apps (like Slack and Mumble) send notification sounds themselves instead of using the notifications server. This means that bubbles can be disabled, but notification sounds cannot.

[danirabbit]

It looks like Corentin's patch was merged into Electron so that those apps should identify themselves correctly in the future: https://github.com/electron/electron/blob/master/brightray/browser/linux/libnotify_notification.cc#L127

[cassidyjames]

This was not fixed by patching the OS settings, as there is not a schema defined for that key; the Notifications plug creates it on the fly. I think we'll have to define the schema for gala-other in the build system for Gala itself instead.

[BNolet]

Should this be closed? Does this mean Juno release is close? :D