Bulk data export

[lyqht]

It will be convenient if users can provide URLs as a multiline string like this

https://github.com/lyqht/mini-qr/issues/32
https://github.com/lyqht/mini-qr/issues/33

and you can choose to save all of the QR codes in a single zip folder.

However, in bulk data export mode,

• the qr code preview should only reflect the first link
• copy qr code should be hidden since it doesn't make sense to copy multiple images.