Returns the icon filepath for this plugin.
        
        :return     <str>

def icon(self):
        """
        Returns the icon filepath for this plugin.
        
        :return     <str>
        """
        path = self._icon
        if not path:
            return ''

        path = os.path.expandvars(os.path.expanduser(path))
        if path.startswith('.'):
            base_path = os.path.dirname(self.filepath())
            path = os.path.abspath(os.path.join(base_path, path))

        return path