Added support for drop-in mods on the UI.

app/assets/js/scripts/overlay.js

@@ -4,6 +4,15 @@
 
 /* Overlay Wrapper Functions */
 
+/**
+ * Check to see if the overlay is visible.
+ * 
+ * @returns {boolean} Whether or not the overlay is visible.
+ */
+function isOverlayVisible(){
+    return document.getElementById('main').hasAttribute('overlay');
+}
+
 /**
  * Toggle the visibility of the overlay.
  *