Simplify fragment transitions for mailbox pairing UI

Now, trying again always starts before scanning, so the user needs to scan the code again.

bramble-api/src/main/java/org/briarproject/bramble/api/mailbox/MailboxPairingState.java

@@ -1,59 +1,25 @@
 package org.briarproject.bramble.api.mailbox;
 
-import javax.annotation.Nullable;
-
 public abstract class MailboxPairingState {
 
-	/**
-	 * The QR code payload that was scanned by the user.
-	 * This is null if the code should not be re-used anymore in this state.
-	 */
-	@Nullable
-	public final String qrCodePayload;
-
-	MailboxPairingState(@Nullable String qrCodePayload) {
-		this.qrCodePayload = qrCodePayload;
-	}
-
 	public static class QrCodeReceived extends MailboxPairingState {
-		public QrCodeReceived(String qrCodePayload) {
-			super(qrCodePayload);
-		}
 	}
 
 	public static class Pairing extends MailboxPairingState {
-		public Pairing(String qrCodePayload) {
-			super(qrCodePayload);
-		}
 	}
 
 	public static class Paired extends MailboxPairingState {
-		public Paired() {
-			super(null);
-		}
 	}
 
 	public static class InvalidQrCode extends MailboxPairingState {
-		public InvalidQrCode() {
-			super(null);
-		}
 	}
 
 	public static class MailboxAlreadyPaired extends MailboxPairingState {
-		public MailboxAlreadyPaired() {
-			super(null);
-		}
 	}
 
 	public static class ConnectionError extends MailboxPairingState {
-		public ConnectionError(String qrCodePayload) {
-			super(qrCodePayload);
-		}
 	}
 
 	public static class UnexpectedError extends MailboxPairingState {
-		public UnexpectedError(String qrCodePayload) {
-			super(qrCodePayload);
-		}
 	}
 }