Google has released a new background data management app called Google Datally.
If you are familiar with the Republic Wireless app with the 2.0 Refund plans, this app is similar as it allows you to turn on or turn off data for the apps on your phone. Edit: The app only controls the background data use for each app. Thus this does not block all data access. The magic is done by using a VPN (the app sets it up for you) and allowing Datally an extra permission to manage the data for each app.
You can download it now from the Google Play Store. https://play.google.com/store/apps/details?id=com.google.android.apps.freighter&hl=en
Here is an overview video of the app: https://www.youtube.com/watch?v=UAdJvXMIlXc