Internal CSS _lim_css layout bug

In the internal controller that displays default Limonade CSS, we should prevents rendering a layout:

  function render_limonade_css()
  {
    option('views_dir', file_path(option('limonade_public_dir'), 'css'));
    $fpath = file_path(params('_lim_css_filename').".css");
    return css($fpath, null);
  }