Allow for use of L.Rectangle()

Leaflet.js has a vector layer option for rectangles, http://leafletjs.com/reference.html#rectangle. The attached patch adds that functionality to the leaflet module, so when defining features, you can just pass in:

    $features[] = array(
      'type' => 'rectangle',
      'bounds' => array(
        'n' => 123,
        's' => 123,
        'e' => 123,
        'w' => 123,
      ),
      'settings' => array(
        'color' => '#ee9900',
        'clickable' => FALSE,
        'fillOpacity' => 0.3,
      ),
    );