Backup export and import

[ArnyminerZ]

Following the discussion #69. Provide an option to export and import the database. This would provide backup functionality for subscriptions, but maybe we want to also move preferences to the database (eg. dark mode toggle) so it's exported together with the subscriptions.

Overall I'd say that the implementation steps would be:

• [x] Create a database import algorithm
• [x] Create a database export algorithm
• [x] Provide an extra option in the overflow menu in subscriptions list. Maybe we can add a "Backup" option, and then show a dialog to choose between import and export, or add a submenu to select this option. However, the second approach would not allow to show a warning to tell the users information about the backup, such as that importing would overwrite the existing data, or that backups are not encrypted.

[ArnyminerZ]

[ArnyminerZ]

device-2023-04-05-160244.webm

[devvv4ever]

Did you test it with multiple entries :) ?