Add Scheduling of Backups/Restores

[Ruthalas]

DESCRIPTION

Request: Allow scheduling of backups and restores (separately).

Providing scheduling options for backups and restores would allow uses to automate syncing their messages with other tools (syncthing/autosync/etc).

Currently one can manually sync the folder between multiple devices, but must backup/restore on each to merge the messages.

This feature would allow a great deal of extensibility to the app.

Thank you for your hard work on this!