qt: apply translator comments to reset options confirmation dialog

Follow-up to dashpay#617. This applies translator strings to the
reset options confirmation dialog and also refactors the way we pass the
strings to the dialog in order to allow the comments to be applied.
Because the strings were being concatenated, we can not apply translator
comments to all of the relevant strings. What we want to do instead is
have a variable in which the translatable strings are appended to using
the QString append function. This satisfies the Qt translator engine and
the comments are then properly applied within the `extracomment` field
in the translation file.

src/qt/optionsdialog.cpp

@@ -286,11 +286,19 @@ void OptionsDialog::on_resetButton_clicked()
 {
     if (model) {
         // confirmation dialog
+        /*: Text explaining that the settings changed will not come into effect
+            until the client is restarted. */
+        QString reset_dialog_text = tr("Client restart required to activate changes.") + "<br><br>";
+        /*: Text explaining to the user that the client's current settings
+            will be backed up at a specific location. %1 is a stand-in
+            argument for the backup location's path. */
+        reset_dialog_text.append(tr("Current settings will be backed up at \"%1\".").arg(m_client_model->dataDir()) + "<br><br>");
+        /*: Text asking the user to confirm if they would like to proceed
+            with a client shutdown. */
+        reset_dialog_text.append(tr("Client will be shut down. Do you want to proceed?"));
+        //: Window title text of pop-up window shown when the user has chosen to reset options.
         QMessageBox::StandardButton btnRetVal = QMessageBox::question(this, tr("Confirm options reset"),
-            tr("Client restart required to activate changes.") + "<br><br>" +
-            tr("Current settings will be backed up at \"%1\".").arg(m_client_model->dataDir()) + "<br><br>" +
-            tr("Client will be shut down. Do you want to proceed?"),
-            QMessageBox::Yes | QMessageBox::Cancel, QMessageBox::Cancel);
+            reset_dialog_text, QMessageBox::Yes | QMessageBox::Cancel, QMessageBox::Cancel);
 
         if (btnRetVal == QMessageBox::Cancel)
             return;