FeatureRequest: Remember verified accounts

[biertz]

Again, many thanks for the project, the ecosystem, and the service.

Another feature request: When sharing more than one collection with another user, I'm asked to compare fingerprints everytime. This is also quite tedious if one has multiple collections that are shared with overlapping groups. When sharing a collection with a person whose fingerprint I already verified, it would be great if the pop-up would just say "You have already verified this user!" and that's it.