Add search fields for # of changed lines.

Based off https://gerrit-review.googlesource.com/#/c/52190, but
implementing the final suggestion of indexing raw delta counts and
allowing arbitrary range queries off of those.

Also upgrade Lucene to 4.8.1 as this was released since the last
schema change (which was on 4.7.0).

Change-Id: Ia8a677e71e133f68eced4c5394df1d23efe7f12a