Support the application/x-keepass2 mime type

The icon is the same as the one (used in this repository) and it is just a placeholder but I certainly want the final one to use the same purplish and white primary and secondary color combinations (Maybe reversed) with the same lock used on the icon app.

EDIT: On first instance the icon won't be added.

Related issue: https://gitlab.gnome.org/World/PasswordSafe/-/issues/197