Activating the plugin and loading the site results in the following error:
document.body is null
A quick and dirty fix is to change the following line:
add_action('wp_head', 'includeJSHeader', 40);
add_action('wp_footer', 'includeJSHeader', 40);
While this fixes the issue, the plugin really should be updated to properly enqueue the script and stylesheet using wp_enqueue_script and wp_enqueue_style, respetively; to properly use capabilities for adding to the menu rather than a number; and to update the editor to more closely match the UI design of WordPress.