views/ui: Rename search-form-pi-widget to ...-row

This keeps it consistent with the other row elements.
views/advanced: Add method selection widget

This widget has an on/off control, in the same manner as the pI
slider.

Issue #240.
views/advanced: Re-arrange search rows

It just looks a bit neater with the two toggle-able widgets before the
remaining text fields. Gives the user a bit of a break from typing.
Merge branch 'issue/240'