Implement backup and restore

[Outlet2048]

Is your feature request related to a problem? Please describe.
Having to recreate everything when switching phones

Describe the solution you'd like
A local backup to file

Describe alternatives you've considered, if any
Cloud backup

Additional context
Backing up and importing from a backup file are very important to me if I actually want to use this app
For now I have to stick to a closed source app for this reason

[DennisBauer]

Thanks for the feature request, I was thinking of some kind of backup system and was anyway planning to add one. Probably just a local backup to a file. Once you have the file you can either put it to a cloud storage provider yourself or transfer it otherwise.
Personally I was also stuck with a closed source app which added more and more ads so I decided to build my own.

[Outlet2048]

Yeah, Export to local file seems to be the best.
I'd transfer it to nextcloud or something myself

Another note
It might be nice to have an option that creates a new backup once the database changes

Example

I add another subscription or change an existing one -> app automatically creates a backup at specified location -> nextcloud app does an auto-upload

That's what an ideal solution looks like to me

[DennisBauer]

@Outlet2048 for the first version I'll add a manual backup and restore option in the settings to a user specified directory.
I created a follow up issue to create automated backups on changes. See #44