Dev - changed project setup for gradle

@DeepDiver1975 Is the new config file valid?
https://github.com/owncloud/News-Android-App/blob/d476e63aa348fb73cd6ffbd6569ef5bc94c6549f/.tx/config

@grote, @mvdan Does it still work with F-Droid?
All dependencies are added as submodules or via maven. The whole project needs to be build via gradle.
You can find more information how to import the project in Android Studio here:
https://github.com/owncloud/News-Android-App/tree/dev#download-and-install--