Initial version of SoundManager for a more central handling of
sound playback All loadSfx() and playSfx() has been replaced
though the codebase to use the new SoundManager.
Fix indentation.
Added a VirtualChannel for syncronous playback of specific
sounds, such as dialogs were the current vox playback should
stop before next vox should play. This moves local sound logics
such in NPC for quest dialogs vox.

Make NPC use the new VirtualChannel playback and remove old
local logic for stopping previous vocal before playing next.
Remove the use of fixed array or sound references and make
items to specify the audio file instead of the hardcoded list
of reference names such as "maille" etc..

Fixes #342
Merge pull request #356 from hean01/soundmanager

Minimal approach for a SoundManager