Upgrade Jsch library to version 0.1.50.

Upgrade to version 0.1.50 to fix JSchException: verify: false that
from time to time.
Move ManualPatchSet class from gerrit-events to gerrit-trigger module

ManualPatchSet is a special event which is only created by gerrit-trigger
to handle patchset triggered manually from Jenkins UI.
Update build-config dependency version
Merge pull request #107 from hugares/jsch-upgrade

Upgrade Jsch library to version 0.1.50.
Merge pull request #108 from hugares/manualpatchsetmove

Move ManualPatchSet class from gerrit-events to gerrit-trigger module