Add keywords to Slices

Attach the keywords used for Settings search to Slices.
Their primary use is helping match synonyms for presenters
which display slices without explicit Uri requests, like a launcher.

This changes:
- Updates database scheme
- Adds to SliceData object
- Grab keywords in the SliceDataConverter
- Set keywords on all slices

Test: robotests
Change-Id: I16c40d2380ffddaf0a87fb1b9cd58e95573b308f
Fixes: 78306195