title: Detect if new install or updated version (Android app)
body: <p>I have an app on the Play Store. I want to put a requirement that if users want to use a certain part of the app, they have to invite a friend before being able to do so. But I only want to impose this restriction to new installs of the app (to be fair to users that have installed the app before the restriction). 
  Sorry for the long intro, my question is how can I find out if the current device has updated the app or is a new install?</p>