Add RoboSpice example

Hi Pierre-Yves,

here is the RoboSpice example we have been talking about in https://github.com/pyricau/CleanAndroidCode/issues/6

It is based on the Retrofit module of RoboSpice, I thought it might be more interesting to you and your peers... ;)

I never had time to try Android Annotations, Otto and Dagger, and really enjoyed them.
Stéphane

PS : let met know if the pull request idea is fine. If so, I'll add tests.