Make the vendor inventort sound always play even if
trader have greetingvocals.
Make NPC vox play on same virtual channel, this will stop previous
vocals before starting playback of another.
Add sfx_close/open to Menu base class so each parent class
can access a open/close sound effect if needed.

Update MenuManager to set default menu close sound for
a few specific menus windows.

Updated the specific menus to play close sound when close
button is pressed.
Merge pull request #359 from hean01/master

Two fixes for sound effects.
Merge pull request #360 from hean01/menusounds

Fixes so that sound is played when close button is pressed on dialogs.
Merge branch 'master' of https://github.com/clintbellanger/flare-engine
Re-added soundfx for opening and closing menus