Added OkHttp, updated gradle

Gradle has been updated. OkHttp has been added as an added feature due to its increased speed, versatility and as explained by author David Gassner "When you use OkHttp, you won't see any change in the functionality of your application, but the app will automatically become more robust, because this library has the ability to recover from failures, a critical capability when you're working with the internet." I have also removed deprecated classes that were not being used by other classes.