Bad UX when trying to import an old backup from a file

[Hocuri]

By increasing DCBACKUP_VERSION, we can make sure that an error will be shown when the user tries to import a new backup into and old Delta Chat version.

This works very nicely for Add-second-device, but for import-file, there are two problems:

1. Even though an error message is shown, the profile is still imported, and accessible via the account switcher.
   Instead, the profile should be deleted if DCBACKUP_VERSION is too new.
2. The error message shown is cryptic, and not localized:

Add-second-device	Import-file