GUI: Disable the Effects menu as it contains absolutely nothing

src/GUI/ui/MainWindow.ui

@@ -54,6 +54,9 @@
     <addaction name="actionFullscreen"/>
    </widget>
    <widget class="QMenu" name="menuEffets">
+    <property name="enabled">
+     <bool>false</bool>
+    </property>
     <property name="title">
      <string>Effects</string>
     </property>