DictonaryGrid should have it's own "append_column" function

It might be nice to be able to more easily add a column to a dictionary grid. Currently the following non-obvious code is required:

    def add_column(self, widget, data=None):
        response, val = prompts.string("New Column","Please select a name for the new column")
        if response == gtk.RESPONSE_OK:
            self.grid.keys.append(val)
            column = conventions.get_column(val,len(self.grid.get_columns()),len(self.grid.keys), True)
            self.grid.append_column(column)
            self.grid._refresh_treeview()

This could easily be append_key(self, key) and then add the column as coded here.