Limit offline username to 16 characters with override

Offline usernames longer than 16 characters won't be able to connect to
LAN games or offline-mode servers, so just don't let it happen.

Add a checkbox to allow people to unrestrict usernames if they want.

Signed-off-by: Jim Ramsay <i.am@jimramsay.com>

launcher/ui/dialogs/OfflineLoginDialog.h

@@ -35,6 +35,7 @@ slots:
     void onTaskProgress(qint64 current, qint64 total);
 
     void on_userTextBox_textEdited(const QString &newText);
+    void on_allowLongUsernames_stateChanged(int value);
 
 private:
     Ui::OfflineLoginDialog *ui;