Update DataRepeater sample to use index property

We didn't have samples that showed the use of the index property to
get the item number, so I've updated DataRepeaterSampler to have
an index at the start of each line.

Enyo-DCO-1.1-Signed-Off-By: Ben Combee (ben.combee@lge.com)
Merge pull request #680 from enyojs/add-index-to-repeater

Update DataRepeater sample to use index property

LGTM

Reviewed-By: Cole Davis (cole.davis@lge.com)