Minimal approach for a SoundManager

This fixes issue #342

- Minimal SoundManager to replace loadSfx() and playSfx() with something that tracks each loaded sound with a id so that shared sounds can be reused to save some memory.

- Rework the NPC dialog vox logic into the SoundManager which was solved with VirtualChannel, if a sound is played on a VirtualChannel when another sound wants to play the previous one is stopped before playing next.

- Remove the hardcoded lists of item sounds, items does now reference sounds by filename instead of the old hardcoded label, this means that all mods items.txt needs to be updated to refer filenames instead of old hardcoded label. (soundmanager branch in my flare-game fork does have a fix for this.)