Accessing [the ParameterChoiceForm page](https://www.ptplot.org/ptplot/parameterchoice) gives HTTP error code 500: internal server error. This is caused by the error below when rendering the template in [`parameterchoice_form()`](https://github.com/CFT-HY/PTPlot/blob/68aaf96eea5b98ecf71f57f6f71995627419ee61/ptplot/views.py#L641): ``` AttributeError: 'ParameterChoiceForm' object has no attribute 'renderer'. Did you mean: 'render'? ```