refactor: add Pubkey, Privkey, NoteId string aliases

This is a non-behavioral change in preparation for the actual switchover
from Strings to Ids. The purpose of this kit is to reduce the size of
the switchover commit which is going to be very large.

damus/Views/SelectWalletView.swift

@@ -10,7 +10,7 @@ import SwiftUI
 struct SelectWalletView: View {
     let default_wallet: Wallet
     @Binding var active_sheet: Sheets?
-    let our_pubkey: String
+    let our_pubkey: Pubkey
     let invoice: String
     @State var invoice_copied: Bool = false
     
@@ -71,6 +71,6 @@ struct SelectWalletView_Previews: PreviewProvider {
     @State static var active_sheet: Sheets? = nil
     
     static var previews: some View {
-        SelectWalletView(default_wallet: .lnlink, active_sheet: $active_sheet, our_pubkey: "", invoice: "")
+        SelectWalletView(default_wallet: .lnlink, active_sheet: $active_sheet, our_pubkey: test_pubkey, invoice: "")
     }
 }