Delete notes that haven't been accessed in a long time

[NikkelM]

The users need to be aware of this. e.g. the settings menu could show the next notes that will be deleted, and a small text at the bottom of the editor could show when the current note will be deleted.

This will rarely be necessary, as there should be enough storage. However, we are unable to know if a note has simply not been accessed in a long time, or if the related message was deleted.

The timer for note deletion should also be reset if a note is viewed, not only when it is edited.