Include the latest patchset only in manual trigger page

Gerrit search in manual trigger page shows all patchsets in a change.
But session needs much memory if result has many rows.
It causes poor PermGen space.

This patch adds a feature that includes the latest patchset only in
search result.

Fix for JENKINS-21064

Task-Url: https://issues.jenkins-ci.org/browse/JENKINS-21064
Merge pull request #182 from rinrinne/latest-patchset

Include the latest patchset only in manual trigger page