windowAttentionHandler.js: make the ignored app check case-

insensitive.  While we're here make it a gsettings array for
convenience.

Quassel used to work - it now returns 'quassel' on my machine.
Enabling the 'focus stealing prevention' switch under windows
behavior solves this, but has too many side effects.

See #5358

data/org.cinnamon.gschema.xml.in

@@ -615,6 +615,11 @@
       </_description>
     </key>
 
+    <key type="as" name="demands-attention-ignored-wm-classes">
+      <default>["skype", "viber", "quassel", "retroshare", "psi-plus", "kadu"]</default>
+      <_summary>WM class names to skip processing for in windowAttentionHandler.js</_summary>
+    </key>
+
   </schema>
 
   <schema id="org.cinnamon.theme" path="/org/cinnamon/theme/"

js/ui/windowAttentionHandler.js

@@ -25,14 +25,11 @@ WindowAttentionHandler.prototype = {
         // We are just ignoring the hint on skip_taskbar windows for now.
         // (Which is the same behaviour as with metacity + panel)
 
+        let wmclass = window.get_wm_class();
+        let ignored_classes = global.settings.get_strv("demands-attention-ignored-wm-classes");
+
         if (!window || window.has_focus() || window.is_skip_taskbar() ||
-            (window.get_wm_class() && (window.get_wm_class().indexOf("Skype") > -1 ||
-                                       window.get_wm_class().indexOf("Viber") > -1 ||
-                                       window.get_wm_class().indexOf("Quassel") > -1 ||
-                                       window.get_wm_class().indexOf("Pidgin") > -1 ||
-                                       window.get_wm_class().indexOf("RetroShare") > -1 ||
-                                       window.get_wm_class().indexOf("Psi-plus") > -1 ||                                       
-                                       window.get_wm_class().indexOf("Kadu") > -1)))
+            (wmclass && (ignored_classes.indexOf(wmclass.toLowerCase()) != -1)))
             return;
 
         try {