Implements #134 source groups

Adds source groups to reconstruct using a new high precision timer abstraction. Gives an ability to precisely control latency and guarantee frame sync. Some work still required to better allow independence between receiving real frames and generate virtual viewpoints. Work also needed to remove callbacks for a clean shutdown.

There are many enhancements to network code efficiency also.

components/common/cpp/src/timer.cpp

@@ -127,7 +127,7 @@ static void trigger_jobs() {
 	// Now use thread jobs to do more intensive callbacks
 	for (auto &j : jobs[kTimerMain]) {
 		if (j.active) {
-			LOG(WARNING) << "Timer job too slow ... skipped for " << ts;
+			DLOG(WARNING) << "Timer job too slow ... skipped for " << ts;
 			continue;
 		}
 		j.active = true;