Remove BottomLeftMenu and supporting bits

The `BottomLeftMenu` component is not used in the new design. This removes the
component and also any images and sub-components that were only used by it.

src/components/structures/LeftPanel.js

@@ -270,7 +270,6 @@ const LeftPanel = React.createClass({
                 </aside>
             </div>
         );
-        // <BottomLeftMenu collapsed={this.props.collapsed}/>
     },
 });