ENYO-591: Provide simpler mechanism for overriding scrollToControl

Our fix for ENYO-591 introduced an overly complex, awkward method
for subkinds of the DataList delegate to override scrollToControl.

Replacing that with something cleaner and simpler. (Thanks to Ryan
Duffy for the suggestion.)

Enyo-DCO-1.1-Signed-Off-By: Gray Norton (gray.norton@lge.com)