Tox

Closes #5714.

Replaces `poison` with the official `qtox`. `Tox` is used as the secondary name since it seems to refer more to the service than the app itself: there are apps for other OSs with different names (`Toxy`, `µTox`, `Toxic`, `Antox`), and they are very consistent with calling this `qTox` in the app itself, not just the bundle’s name.