missing features dlg: better update hint (#3352)

## Short roundup of the initial problem
People missed the hint on how to resolve missing features on their own, because update hint was hidden behind the `Show details` label.

## What will change with this Pull Request?
- Update hint is more prominently placed and not hidden behind a label
- It's translatable now
- Wording update to reflect UI change

## Screenshots
<!-- simply drag & drop image files directly into this description! -->
- before
![missing_features](https://user-images.githubusercontent.com/9874850/43153756-74cfd9f0-8f72-11e8-9e0f-fbf47b13f324.png)
- after
![missing_features_new](https://user-images.githubusercontent.com/9874850/43153761-78bec4e0-8f72-11e8-9853-ccc1ecb7f558.png)

cockatrice/src/window_main.cpp

@@ -362,12 +362,12 @@ void MainWindow::loginError(Response::ResponseCode r,
             for (int i = 0; i < missingFeatures.size(); ++i)
                 formattedMissingFeatures.append(QString("\n     %1").arg(QChar(0x2022)) + " " +
                                                 missingFeatures.value(i));
-            formattedMissingFeatures.append("\nTo update your client, go to Help -> Check for Updates.");
 
             QMessageBox msgBox;
             msgBox.setIcon(QMessageBox::Critical);
             msgBox.setWindowTitle(tr("Failed Login"));
-            msgBox.setText(tr("Your client seems to be missing features this server requires for connection."));
+            msgBox.setText(tr("Your client seems to be missing features this server requires for connection.") +
+                           "\n\n" + tr("To update your client, go to 'Help -> Check for Client Updates'."));
             msgBox.setDetailedText(formattedMissingFeatures);
             msgBox.exec();
             break;