Resolve issues with foreground tasks getting cancelled

[bjester]

Summary

• Adds dependency androidx.lifecycle:lifecycle-service:2.7.0 since SystemForegroundService relies on it (possible this was the problematic oversight)
• Removes some unused imports
• Adds PythonProvider class which implements AutoCloseable for use with try-with-resources, to provider the android context to the python side, and automatically ensure we don't create context memory leaks
• Updates ContextUtil to utilize the PythonProvider if it's active
• Refactors work manager worker logic into abstract base class and makes foreground worker a regular Worker instead of RemoteListenableWorker
• Re-adds setForegroundAsync that was mistakenly deleted, but does not call it repeatedly-- calling it repeatedly seemed to have no benefit against the issue but to spam the logs
• Goes back to having a single android notification for tasks, and since foreground tasks require an integer ID, it converts the task request UUID to an integer using CRC32
• Removes WorkerService which was a RemoteWorkerService for running RemoteListenableWorkers
• Adds observer pattern to task worker implementation so task update calls go through it, which is a Java object that should only exist in the same task's thread
• Adds onProgressUpdate hook method to worker base class which is called when the task's progress is updated, and by default calls setProgressAsync and updates the notification (this may be the true fix)
• Fixes order of operation issue after switching to // division instead of using math.floor(...) changed in https://github.com/learningequality/kolibri-installer-android/issues/204
• Adds android.permission.POST_NOTIFICATIONS permission and check for it since Android Studio was complaining about it missing (I don't recall this happening previously)

References

Fixes https://github.com/learningequality/kolibri-installer-android/issues/205

[rtibbles]

Goes back to having a single android notification for tasks, and since foreground tasks require an integer ID, it converts the task request UUID to an integer using CRC32

Nice!