Added Hardcore Warning Widget

This widget will be used in several places to notify the player that a feature has been disabled because hardcore mode is on. It includes a button to open the Achievement Settings so that Hardcore Mode may be turned off. Also included is the framework required to open AchievementsWindow specifically on the Settings tab.

Source/Core/DolphinQt/MainWindow.cpp

@@ -1971,6 +1971,12 @@ void MainWindow::ShowAchievementsWindow()
   m_achievements_window->raise();
   m_achievements_window->activateWindow();
 }
+
+void MainWindow::ShowAchievementSettings()
+{
+  ShowAchievementsWindow();
+  m_achievements_window->ForceSettingsTab();
+}
 #endif  // USE_RETRO_ACHIEVEMENTS
 
 void MainWindow::ShowMemcardManager()