Hook up CMS.ServerError to new alerting system

cms/static/js/views/server_error.js

 CMS.ServerError = function(model, error) {
-	// this handler is for the client:server communication not the validation errors which handleValidationError catches
-	window.alert("Server Error: " + error.responseText);
+    var m = new CMS.Models.Alert({
+        "type": "error",
+        "title": "Server Error",
+        "message": error.responseText,
+        "close": true
+    });
+    new CMS.Views.Alert({model: m}).render();
 };