Adding ItemListener wrapper

Status: WIP

Currently failing to run specs:

```
✗ bundle exec rspec
NameError: missing class or uppercase package name (`org.kohsuke.stapler.StaplerProxy')
  get_proxy_or_package_under_package at org/jruby/javasupport/JavaUtilities.java:54
                      method_missing at file:/Users/drnic/.rvm/rubies/jruby-1.7.3/lib/jruby.jar!/jruby/java/java_package_module_template.rb:14
                               Proxy at /Users/drnic/Projects/ruby/gems/jenkins.rb/ruby-runtime/lib/jenkins/plugin/proxy.rb:17
                         module_eval at org/jruby/RubyModule.java:2291
```

Need to figure out how to add more Java packages into jenkins.rb