Automatic backup

[Spiny150]

The Idea :
Add an option to automatically create backups at a selected time interval.

Why it's useful :
Users could then sync their files to their preferred cloud storage space, avoiding data loss if the user breaks or loses their phone.

Additional note :
Older backups would probably have to be deleted for reasons of storage constraints.

[leonlatsch]

Hey,

Something along these lines is already considered in #354

Also #197 plans to have the possibility to store everything in an external location (cloud) aswell.