Add project skeleton

Review Request #8919 — Created May 5, 2017 and submitted — Latest diff uploaded

Information

gerrit-reviewboard-plugin
master
2dc7583...

Reviewers

This patch sets up the project skeleton. The project is built with maven
and can be built according to the instructions in README.md.

Built with mvn package. I was able to see my plugin in Gerrit's plugin
API.