STYLE: Rename DiffusionTensorScalarMeasurements option name

The original option name was misleading, it has been renamed to better
guide the user.

Fixes #3591

Co-authored-by: Sonia Pujol <spujol@bwh.harvard.edu>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22885 3bd1e089-480b-0410-8dfb-8563597acbee