v4.0.0: Processing improvements

Breaking Changes:

• Min SDK version was updated to 21
• Constructor of AppMetricaPushTracker changed from AppMetricaPushTracker() to AppMetricaPushTracker(Context)
• Interface PushServiceController was updated. Specifically, the method getTitle has been renamed to getTransportId, and methods getExecutionRestrictions and shouldSendToken have been added.

Enhancements and Corrections:

• Improvements in deliverability and processing speed of push notifications

Full Changelog: v3.3.0...v4.0.0