Add loadEventCallback

The snippet allows for a callback on certain methods. Since the React SDK handles _ps("load") under the hood we need allow users to specify an error handling callback for this method.

src/PSClickWrap.js

@@ -220,6 +220,7 @@ class PSClickWrap extends React.Component {
       signerIdSelector,
       snapshotLocation,
       allowDisagreed,
+			loadEventCallback,
     } = this.props;
     const options = {
       ...(allowDisagreed !== undefined && { allow_disagreed: allowDisagreed }),
@@ -255,6 +256,7 @@ class PSClickWrap extends React.Component {
         if (!isDynamic) group.render();
         this.registerEventListeners(key);
       }
+			loadEventCallback && loadEventCallback(err, group);
     };
 
     if (customData) {
@@ -334,6 +336,7 @@ PSClickWrap.propTypes = {
     (props) => props.hasOwnProperty('onInvalid'),
     PSClickWrap.MUST_SET_ALLOW_DISAGREED,
   ),
+	loadEventCallback: PropTypes.func,
   debug: PropTypes.bool,
   onAll: PropTypes.func,
   onSent: PropTypes.func,