Conversion to gradle buildsystem

I've converted the project to the gradle build system - not sure what the status of gradle is with eclipse but the recommendation from google is to use gradle going forward. Also making eclipse projects build in Android Studio is a pain in the arse.

Theoretically you should be able to keep your repo using the old build style and still merge any PR's from me because git should have tracked the moved files correctly - so it's your call - either way feel free to check out my branch and test the gradle build system if you aren't already using it elsewhere - all you should have to do after installing android studio and importing is setting a local.properties file in the root of the repo as such

$ cat local.properties
sdk.dir = /Applications/Android Studio.app/sdk