add approval widget for extracted features

The "xray features view" should have an associated mechanism for the clinician to approve extracted features.

This approval should somehow enter the record, being remembered and making it into any generated reports.
I'm getting a bit ahead of myself: for now this issue is about having a widget in place to indicate approval.

Start at the xray features view and trace how extracted features are displayed. Add a widget that lets the clinician indicate approval; this first phase is complete when the approval control is present in that view.

Written by the indexing model from the issue text.