replacing javadoc, to not show example class

Today we, unfortunately, show the demo/example class:
http://aerogear.org/docs/specs/aerogear-simplepush-java-client/package-frame.html

This PR replace the current doc, with 'correct' doc.


There is also a PR that fixes the issue on the project itself: https://github.com/aerogear/aerogear-simplepush-java-client/pull/4