[PVR] Fix PVR manager start/stop races

[ksooo]

Stopping PVR Manager must follow the strict two-step logic for all (!) of its sub components.

1. Stop all sub components (means, stop their worker threads to hold processing)
2. Unload all sub components (clearing all data)

Starting must follow the exact revere logic

1. Load all sub components (loading their data from clients and/or database)
2. Start all sub components

This was not implemented properly for CPVRTimers and CPVREpgContainer components and should be fixed by this PR.

Runtime-tested on macOS and Android, latest kodi master. I had a testcase reproducible on my Mac which led to all kind of errors and even crashes.

[phunkyfish]

Nice