Add follower count using NIP-45 to Damus

Create a PR to use NIP-45 COUNT verb to get follower count on the profile screen, using a filter like {"kinds":[3],"#p":["pubkey"]}.

Not many relays implement NIP-45, wss://relay.nostr.band is a good option. There should probably be a way for users to choose the counting relay, maybe on the Settings screen.

Questions about implementation details should be discussed with jb55, the bounty will be paid after PR is accepted.