Claim cards after importing data from another session

[NearW]

Description

As a Retro user, I want to get ownership of my cards again when an old session is imported into a new session again, so that I can continue working / editing my cards.

Acceptance Criteria

• Importing an old state should clear owners of cards (make each entry to undefined, but keep the entries, so that we now how many ids are left to claim)
• Cards with missing owners can be claimed by anyone who did not claim the card before
• Claiming icon is added to the card
• Claiming a card will add you as an owner of that card