Remove manual lifetime-management in the sound manager.

[phosit]

Manual lifetime-management(new/delete) is error-prone. Unfortunately it is used a lot in the SoundManager. I think we should do that bevore we make use of the TaskManager to make the transition simpler.

The simplest way is to use std::unique_ptr but that does IMO only "address the symptom". When possible we should implace the object (use ItemsList instead of std::unique_ptr<ItemsList>.