Import / export address labels

[kristapsk]

There is a new BIP for this, from Craig Raw, Sparrow Wallet dev - https://github.com/bitcoin/bips/blob/master/bip-0329.mediawiki.

There is also old alternaive standard for this by Trezor - https://github.com/satoshilabs/slips/blob/master/slip-0015.md.

Looks to me as something we could implement in some way in future. Should also not be too difficult.