use the new sender api

@matzew @sebastienblanc @edewit  to test the alpha.1, updated the quick-start to also use the new sender api. (use @edewit current open PR https://github.com/aerogear/aerogear-unifiedpush-java-client/pull/64)

Feel free to close though and open a new one at a later time when you think is more appropriate.