Add NIP-50 search to Damus

Create a PR to add search over kind:1 events into Damus, there is already a tab and a search box, need to forward typed string using NIP-50 to the relay and render results.

Not many relays implement NIP-50, wss://relay.nostr.band is a good option. There should probably be a way for users to choose the search relay, maybe on the Settings screen.

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