Don't update load and save buttons.

This use of shouldComponentUpdate is wrapping the incorrect use of bind
in the mapStateToProps call.

src/containers/load-button.jsx

@@ -14,6 +14,9 @@ class LoadButton extends React.Component {
             'handleClick'
         ]);
     }
+    shouldComponentUpdate () {
+        return false;
+    }
     handleChange (e) {
         const reader = new FileReader();
         reader.onload = () => this.props.loadProject(reader.result);

src/containers/save-button.jsx

@@ -14,6 +14,9 @@ class SaveButton extends React.Component {
             'handleClick'
         ]);
     }
+    shouldComponentUpdate () {
+        return false;
+    }
     handleClick () {
         const json = this.props.saveProjectSb3();