Use Opus for VoIP

Server/client VoIP protocol is handled by adding new cvars
cl_voipProtocol and sv_voipProtocol, sv_voip and cl_voip
are used to auto set/clear them. All users need to touch
are cl/sv_voip as 0 or 1 just like before.

Old Speex VoIP packets in demos are skipped.
New VoIP packets are skipped in demos if sv_voipProtocol
doesn't match cl_voipProtocol.

Notable difference between usage of speex and opus codecs,
when using Speex client would be sent 80ms at a time.
Using Opus, 60ms is sent at a time. This was changed because
the Opus codec supports encoding up to 60ms at a time.
(Simpler to send only one codec frame in a packet.)

code/client/cl_input.c

@@ -788,7 +788,7 @@ void CL_WritePacket( void ) {
 	{
 		if((clc.voipFlags & VOIP_SPATIAL) || Com_IsVoipTarget(clc.voipTargets, sizeof(clc.voipTargets), -1))
 		{
-			MSG_WriteByte (&buf, clc_voip);
+			MSG_WriteByte (&buf, clc_voipOpus);
 			MSG_WriteByte (&buf, clc.voipOutgoingGeneration);
 			MSG_WriteLong (&buf, clc.voipOutgoingSequence);
 			MSG_WriteByte (&buf, clc.voipOutgoingDataFrames);
@@ -809,7 +809,7 @@ void CL_WritePacket( void ) {
 				MSG_Init (&fakemsg, fakedata, sizeof (fakedata));
 				MSG_Bitstream (&fakemsg);
 				MSG_WriteLong (&fakemsg, clc.reliableAcknowledge);
-				MSG_WriteByte (&fakemsg, svc_voip);
+				MSG_WriteByte (&fakemsg, svc_voipOpus);
 				MSG_WriteShort (&fakemsg, clc.clientNum);
 				MSG_WriteByte (&fakemsg, clc.voipOutgoingGeneration);
 				MSG_WriteLong (&fakemsg, clc.voipOutgoingSequence);