add a clear all button to the sign message page

src/qt/forms/messagepage.ui

@@ -101,12 +101,12 @@
        <italic>true</italic>
       </font>
      </property>
-     <property name="text">
-      <string>Click &quot;Sign Message&quot; to get signature</string>
-     </property>
      <property name="readOnly">
       <bool>true</bool>
      </property>
+     <property name="placeholderText">
+      <string>Click &quot;Sign Message&quot; to get signature</string>
+     </property>
     </widget>
    </item>
    <item>
@@ -139,6 +139,20 @@
        </property>
       </widget>
      </item>
+     <item>
+      <widget class="QPushButton" name="clearButton">
+       <property name="toolTip">
+        <string>Reset all sign message fields</string>
+       </property>
+       <property name="text">
+        <string>Clear all</string>
+       </property>
+       <property name="icon">
+        <iconset resource="../bitcoin.qrc">
+         <normaloff>:/icons/remove</normaloff>:/icons/remove</iconset>
+       </property>
+      </widget>
+     </item>
      <item>
       <spacer name="horizontalSpacer">
        <property name="orientation">

src/qt/messagepage.cpp

@@ -105,3 +105,10 @@ void MessagePage::on_signMessage_clicked()
     ui->signature->setText(QString::fromStdString(EncodeBase64(&vchSig[0], vchSig.size())));
     ui->signature->setFont(GUIUtil::bitcoinAddressFont());
 }
+
+void MessagePage::on_clearButton_clicked()
+{
+    ui->signFrom->clear();
+    ui->message->clear();
+    ui->signature->clear();
+}

src/qt/messagepage.h

@@ -33,6 +33,7 @@ private slots:
 
     void on_signMessage_clicked();
     void on_copyToClipboard_clicked();
+    void on_clearButton_clicked();
 };
 
 #endif // MESSAGEPAGE_H