Notification retention days
User should be able to select for how many days notifications should stay on the phone. The app should implement the following behaviour:
- the user should be able to select for how many days he wants to keep the notifications on the phone
- when the retention period of a notification is expired, the notification should disappear from the phone but stay on the server
- if the user changes the retention period, the notification should be re-synced
- pinned notifications should not have retention period, they stay until they are unpinned:
- if a notification is pinned, then user can see it even if retention period is passed
- if user unpins a notification, and the retention period is passed, it should disappear