Migrate from v2 to v3

v3 of the Localytics Android SDK represents a substantial architectural change as well as a simplification of the API. To ensure proper initialization and push message tracking, we now require the use of a custom Application class for integration. Please follow the steps below to make the appropriate adjustments.

Most notably, you no longer need to create and maintain a LocalyticsSession object. Instead, all calls to the library API run through class-level methods of the Localytics class. In addition, all methods which were previously part of LocalyticsSession and LocalyticsAmpSession are now available combined under Localytics.

v3 of the Localytics Android SDK also lays the foundation for upcoming features. Architecture updates allow us to quickly introduce new features without requiring backwards-incompatible changes. The v3 SDK supports

background event tagging, enabling you to track events that occur outside a session, and
new Profile APIs, enabling you to increment, decrement, add to set, and remove from set.

Changes to the method signatures make the iOS and Android Localytics SDKs almost identical. We've aligned the method signatures on iOS and Android, making it easier to keep your integrations up to date. The new method signatures also simplify development in new languages and alternative platforms.

Profiles data now defaults to an app-level scope. Previously all Profiles data defaulted to an org-level scope.

Add Google Play Services in your project for GCM support. More information on Google Play Services can be found here.
Add the PushTrackingActivity to your AndroidManifest.xml. This Activity is used to track open rates for push notifications.
```
<activity android:name="com.localytics.android.PushTrackingActivity"/>
```
Follow the steps for automatic or manual migration.