app.py/preprocessing()
   -> source/forms/views.py/run_preprocessing(request, adata, step_log)
      -> source/forms/forms.py/getPreprocessForm()
      -> templates/preprocessing.html
         -> templates/superform.html

* step_log defined in app.py, keeps track whether pre-processing was run.
    -> If not run, then run_preprocessing shows just the form.
    -> If has run, shows banner that preprocessing complete.

* If attempt to run_preprocessing() when adata not yet loaded, shows banner
    indicating need to upload the data first.

* source/forms/forms.py/getPreprocessForm() generates a WTForm class using a
    general WTForm generator, as defined in:
    source/forms/forms.py/createSuperForm()

* templates/preprocessing.html is the preprocessing page, which also injects
    in a form to display using templates/superform.html.

* templates/superform.html renders a general WTForm that was created using
    the source/forms/forms.py/createSuperForm() function, thereby allowing
    easy generation of new forms if need to add extra information.