Private Zaps

This adds private zaps, which have messages and authors encrypted to
the target. Keys are deterministically generated so that both the
receiver and sender can decrypt.

Changelog-Added: Private Zaps

damus/Views/Zaps/ZapsView.swift

@@ -21,7 +21,7 @@ struct ZapsView: View {
             LazyVStack {
                 ForEach(model.zaps, id: \.event.id) { zap in
                     ZapEvent(damus: state, zap: zap)
-                        .padding()
+                        .padding([.horizontal])
                 }
             }
         }