#1 Remove hard-coded references to sounds from UserAgent

[Brent]

local.ua.UserAgent has hard-coded references to:

MEDIA_PATH
CLIP_ON
CLIP_OFF
CLIP_RING

Minimal solution is to make these values configurable. It may be preferable to remove any audio that isn't part of a conversation from the UserAgent class all together. This class isn't inherently a GUI class and probably shouldn't be responsible for playing audio alerts to the human user.