Add product flavor demo code.
Add product flavor demo code.

KarthicK10/AND_Project_4_BuildItBigger,DevDoug/AndroidNanoDegreeProjectFour,KarthicK10/AND_Project_4_BuildItBigger,Sushant-M/Joke_Telling_App,DevDoug/AndroidNanoDegreeProjectFour,Wertros/GradleTutorial,udacity/ud867,Sushant-M/Joke_Telling_App,udacity/ud867,Wertros/GradleTutorial,SethsApps/ud867,SethsApps/ud867