Update to @tmccarthy9 Android Push Tutorial (AGPUSH-21)

based on @tmccarthy9 work in his [PR](https://github.com/aerogear/aerogear.org/pull/99) I have updated the guide to:

- sync the server curl commands with the latest dev
- removed sections about setting up Eclipse and the Build
- 'Your first Android/Push app' was completely revamped. The user now builds a sample application and in the process the API is described. I think having the developer to build an app will help comprehend better how the push mechanism works.
- various other syncs and updates

Thanks @tmccarthy9 for the initial work!