Fix notifications on Android

[clangenb]

Changes:

• For some reason, we didn't check if notification permissions were given on Android. This is now checked upon startup and the user is prompted to allow notifications.

Fix Scheduled Notifications on Android

• Fix android manifest to show scheduled permissions and to persist scheduled notifications after a reboot
• Android > 13 doesn't allow exact scheduling of notifications, which resulted in an error. We simply relaxed our scheduling to inexact, as we are not building a precise alarm app.