Create Template Java Project

As we write more and more Java code we need to have some common conventions for this code.

After this is complete we can work on https://github.com/elastic/logstash/issues/5353 and https://github.com/elastic/logstash/issues/5354

We need to create a sample logstash plugin rubygem (maybe modify https://github.com/logstash-plugins/logstash-output-example) that includes java extensions setup in a standard way.
- [ ] Gradle
- [ ] Include .idea plugin for those who like it
- [ ] Java 8 Language Level (look into LS 2.x support terms)
- [ ] Standard src/test folder locations
- [ ] Test java code with Test Unit
- [ ] Test ruby code with rspec
- [ ] Use Hamcrest Matchers
- [ ] Should have correct .gitignore
- [ ] Namespace should be org.logstash
- [ ] Packages should not publish anywhere (e.g. Maven Central) yet.
- [ ] You should not have to publish before you can build stuff.
- [ ] Import all Elasticsearch compile flags (except security manager)