add rememberFocusIndex property to moonstone/DataList
add rememberFocusIndex property to moonstone/DataList

In scenarios in which the DataList is re-rendered (e.g. when inside
a LightPanel that has moved offscreen), the list forgets the last
spotted row. Setting rememberFocusIndex to true causes it to remember.

Issue: ENYO-2744
Enyo-DCO-1.1-Signed-off-by: Ryan Duffy (ryan.duffy@lge.com)

enyojs/moonstone