[Azoth Sarin] Do not pass the direction on calling.
[Util] Default ctor for ConcurrentException.
[Azoth Sarin] ThreadExceptionBase -> TextExceptionBase.
[Azoth Sarin] UnknownFriendException.
[Azoth Sarin] Reworked ScheduleFunction().

Return QFuture<void> for functions without return type.
[Azoth Sarin] Actually create the AudioCallDevice.
[Azoth Sarin] Added CallAnswerException.
[Azoth Sarin] Probably support building without ENABLE_MEDIACALLS.