Dump/import of board posts

[Cappucirno]

I'd like to be able to dump specific board posts to a file and then import them into another save's board. Pretty niche thing, but I figure it's probably not too difficult to add since you can already edit boards directly. I want this because I have multiple saves of the same island and sometimes visitors will leave drawings or messages, but I'll often discard the save and import another over it so those would be lost. So I'd like a way to move the posts between saves so they're always there so visitors can see them later.