hide the gap limit and request a birth date for a silent payments wallet in the terminal

### src/main/java/com/sparrowwallet/sparrow/terminal/wallet/AdvancedDialog.java
@@ -2,6 +2,7 @@
 
 import com.googlecode.lanterna.TerminalSize;
 import com.googlecode.lanterna.gui2.*;
+import com.sparrowwallet.drongo.policy.PolicyType;
 import com.sparrowwallet.drongo.wallet.Wallet;
 import com.sparrowwallet.sparrow.io.Storage;
 import com.sparrowwallet.sparrow.wallet.WalletForm;
@@ -39,9 +40,14 @@ public AdvancedDialog(WalletForm walletForm) {
         birthDate = new TextBox().setValidationPattern(Pattern.compile("[0-9\\-/]*"));
         mainPanel.addComponent(birthDate);
 
-        mainPanel.addComponent(new Label("Gap limit"));
-        gapLimit = new TextBox().setValidationPattern(Pattern.compile("[0-9]*"));
-        mainPanel.addComponent(gapLimit);
+        //A silent payments wallet derives no addresses to look ahead over, and getGapLimit() returns zero whatever is stored
+        if(wallet.getPolicyType() == PolicyType.SINGLE_SP) {
+            gapLimit = null;
+        } else {
+            mainPanel.addComponent(new Label("Gap limit"));
+            gapLimit = new TextBox().setValidationPattern(Pattern.compile("[0-9]*"));
+            mainPanel.addComponent(gapLimit);
+        }
 
         Panel buttonPanel = new Panel();
         buttonPanel.setLayoutManager(new GridLayout(2).setHorizontalSpacing(1));
@@ -60,7 +66,9 @@ public AdvancedDialog(WalletForm walletForm) {
             birthDate.setText(DATE_FORMAT.format(wallet.getBirthDate()));
         }
 
-        gapLimit.setText(Integer.toString(wallet.getGapLimit()));
+        if(gapLimit != null) {
+            gapLimit.setText(Integer.toString(wallet.getGapLimit()));
+        }
 
         birthDate.setTextChangeListener((newText, changedByUserInteraction) -> {
             try {
@@ -73,19 +81,21 @@ public AdvancedDialog(WalletForm walletForm) {
             }
         });
 
-        gapLimit.setTextChangeListener((newText, changedByUserInteraction) -> {
-            try {
-                int newValue = Integer.parseInt(newText);
-                if(newValue < 0 || newValue > 1000000) {
+        if(gapLimit != null) {
+            gapLimit.setTextChangeListener((newText, changedByUserInteraction) -> {
+                try {
+                    int newValue = Integer.parseInt(newText);
+                    if(newValue < 0 || newValue > 1000000) {
+                        return;
+                    }
+
+                    wallet.setGapLimit(newValue);
+                    apply.setEnabled(true);
+                } catch(NumberFormatException e) {
                     return;
                 }
-
-                wallet.setGapLimit(newValue);
-                apply.setEnabled(true);
-            } catch(NumberFormatException e) {
-                return;
-            }
-        });
+            });
+        }
     }
 
     private void onChangePassword() {

### src/main/java/com/sparrowwallet/sparrow/terminal/wallet/WatchOnlyDialog.java
@@ -3,6 +3,7 @@
 import com.googlecode.lanterna.TerminalPosition;
 import com.googlecode.lanterna.TerminalSize;
 import com.googlecode.lanterna.gui2.*;
+import com.googlecode.lanterna.gui2.dialogs.TextInputDialogBuilder;
 import com.sparrowwallet.drongo.ExtendedKey;
 import com.sparrowwallet.drongo.KeyDerivation;
 import com.sparrowwallet.drongo.OutputDescriptor;
@@ -18,11 +19,15 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import java.text.ParseException;
+import java.text.SimpleDateFormat;
 import java.util.*;
 
 public class WatchOnlyDialog extends NewWalletDialog {
     private static final Logger log = LoggerFactory.getLogger(WatchOnlyDialog.class);
 
+    private static final SimpleDateFormat DATE_FORMAT = new SimpleDateFormat("yyyy-MM-dd");
+
     private final TextBox descriptor;
     private final Button importWallet;
 
@@ -143,9 +148,31 @@ private List<Wallet> getWalletFromOutputDescriptor(String text) {
         OutputDescriptor outputDescriptor = OutputDescriptor.getOutputDescriptor(text);
         Wallet wallet = outputDescriptor.toWallet();
         wallet.setName(walletName);
+        if(wallet.getPolicyType() == PolicyType.SINGLE_SP && wallet.getBirthDate() == null && wallet.getBirthHeight() == null) {
+            wallet.setBirthDate(requestBirthDate());
+        }
+
         return List.of(wallet);
     }
 
+    private Date requestBirthDate() {
+        TextInputDialogBuilder builder = new TextInputDialogBuilder().setTitle("Wallet Birth Date");
+        builder.setDescription("Silent payments are scanned for from this date onwards." + System.lineSeparator() + "Enter the date this wallet was created as " + DATE_FORMAT.toPattern() + ".");
+        builder.setInitialContent(DATE_FORMAT.format(new Date()));
+
+        String enteredDate = builder.build().showDialog(SparrowTerminal.get().getGui());
+        if(enteredDate == null || enteredDate.isBlank()) {
+            return null;
+        }
+
+        try {
+            return DATE_FORMAT.parse(enteredDate.trim());
+        } catch(ParseException e) {
+            log.warn("Could not parse the birth date entered for " + walletName);
+            return null;
+        }
+    }
+
     private List<String> splitString(String stringToSplit, int maxLength) {
         String text = stringToSplit.replaceAll("\\s+", "");
         if(stringToSplit.endsWith("\n")) {