Add way to modify columns and retain filters

[vidartf]

Currently if you want to modify the columns that are displayed, you need to update the colmnNames on the model, and then re-init the panel widget. This causes the filter inputs to be reset, and causes flicker when re-initing.

Ideally, we could change the columns, and retain the filters of any columns that remain visible (any filters on hidden columns will as a matter of necessity be cleared).