Titration processing widget assumes increasing mode

Currently if a titration table from 'fixed' mode is connected to a processing widget, then an error is thrown. The error is because the processing widget requires a 'dilution factor' column, which is not included in the fixed mode.

Start by reproducing the issue with a titration table from fixed mode connected to the processing widget, then inspect where the widget requires the dilution factor column. Done means fixed-mode tables no longer throw an error when connected, while increasing-mode processing continues to work.

Written by the indexing model from the issue text.