Version 1.2.6

• Make the license in Java files clearer, see #422
• Use own internal monitor for synchronizing access to variables in order to avoid deadlocks when using the library, see #414
• Cleanup jobs in the database if no job creator returns an instance during execution, see #413
• Make sure that the JobManager is created when canceling jobs, see #442
• Don't crash on Android 4.X with the recent Google Play Services, see #415
• Explain the relation to WorkManager, see here