Start a new filewatcher at the specified path.

def post(self, *args):
        """
        Start a new filewatcher at the specified path.
        """
        filepath = self.get_body_argument('filepath')
        if not self.fs.exists(filepath):
            raise tornado.web.HTTPError(404)

        Filewatcher.add_directory_to_watch(filepath)
        self.write({'msg':'Watcher added for {}'.format(filepath)})