Convert icons to masks

so they're a sensible colour in other themes

src/components/views/dialogs/BaseDialog.js

@@ -75,8 +75,12 @@ export default createReactClass({
         // If provided, this is used to add a aria-describedby attribute
         contentId: PropTypes.string,
 
-        // optional additional class for the title element
-        titleClass: PropTypes.string,
+        // optional additional class for the title element (basically anything that can be passed to classnames)
+        titleClass: PropTypes.oneOfType([
+            PropTypes.string,
+            PropTypes.object,
+            PropTypes.arrayOf(PropTypes.string),
+        ]),
     },
 
     getDefaultProps: function() {