Add RetroLambda to project and fix use of HomeFragment

App was skipping the use of HomeFragment entirely, called
the HomeActivity onGoButtonPressed directly via the onClick
xml attribute. When using a fragment with activity,
ensure the following:
  - Activity extends android.support.v4.app.FragmentActivity
  - XML fragment definition has the class attribute properly set
  - Your Activity uses the activty xml layout
Add java env setup instructions to README
Add attribution notes to VIPTabBarActivity TabsAdapter class
Move retrolambda plugin to app build.gradle