[aerogear-dev] GCM Topics feature branch

So it looks like the work for properly supporting topics is going to grow. So far we have identified two areas for improvement already : * lfryc and I met this afternoon and discussed how to handle topic failures where calling back to registrationIds is appropriate. He has some refactors he wants to make. * Last night on the -users list a community member brought up some use case we have to consider as well. Specifically around how `alias` and `deviceType` interact with topics. In the spirit of keeping the PRs manageable, I propose we create a feature branches for topics in aerogear/aerogear-unifiedpush-server and aerogear/aerogear-android-push. Barring strong opinions against this, I will create these branches and move my PRs appropriately.