Added automatic tracking of common mobile events

With this release we are adding automatic tracking of common mobile events. These events include tracking app sessions, first app opens, in-app purchases, app updated, and app crashed.
The feature will be rolled out slowly to all our users, and can be turned on in Project settings under Autotrack.
To configure the tracking of app sessions, we now expose two new properties, minimumSessionDuration and maximumSessionDuration. These properties provide lower and upper bounds on the session lengths that your app will track.