Serve plugin page

    :param plugin_key: Which plugin page to server; if None -> landing page
            (default: None)
    :type plugin_key: None | unicode

def plugin(plugin_key=None):
    """
    Serve plugin page

    :param plugin_key: Which plugin page to server; if None -> landing page
            (default: None)
    :type plugin_key: None | unicode
    """
    p = None
    if plugin_key:
        try:
            p = db_plugin_instance.plugin_get(plugin_key)
        except KeyError:
            logger.error(u"Plugin '{}' not found".format(plugin_key))

    return render_template("plugin.html", title="Plugins", plugin=p)