Easy way to open the app via a lockscreen notification

[mathjeff]

(As mentioned in https://www.reddit.com/r/SomebodyMakeThis/comments/mktnpm/sanctuary_app_a_super_effective_pomodorolike/ )

It would be interesting if ActivityRecommender provided users the option to request a notification on the locks creen of their phone, that when clicked, opens ActivityRecommender directly.

Hopefully this would:
A) make it slightly faster to open ActivityRecommender in the case where the phone is already unlocked
B) make the process of opening ActivityRecommender feel slightly more streamlined and make it even easier to avoid getting distracted

I think we probably want this feature to be disabled by default because if all apps did this it would be too many notifications on the lock screen. I think we probably want this feature to be configured similarly to how the changing of a theme is configured: the setting can be saved into the user's data file and ActivityRecommender can read it to determine whether to show a notification.

I'm not sure when the most appropriate time to do this reading would be. It might be possible to run something in the background that creates this notification, but it's probably much simpler for the notification to be created only once the user opens the app. This could even be a good thing because it may be less annoying if the notification only appears after ActivityRecommender has been opened