Looks up the plugin for the given column.
        
        :param      column | <orb.Column>
        
        :return     <XOrbQueryPlugin> || None

def plugin(self, column):
        """
        Looks up the plugin for the given column.
        
        :param      column | <orb.Column>
        
        :return     <XOrbQueryPlugin> || None
        """
        base = ColumnType.base(column.columnType())
        
        a = (column.columnType(), column.name())
        b = (column.columnType(), None)
        c = (base, column.name())
        d = (base, None)
        e = (None, column.name())
        f = (None, None)
        
        for check in (a, b, c, d, e, f):
            try:
                return self._plugins[check]
            except KeyError:
                continue
        
        return None