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/rgbd-sources/src/snapshot.cpp

@@ -458,12 +458,10 @@ Snapshot SnapshotReader::readArchive() {
 	else {
 		LOG(INFO) << "Using old format snapshot archive";
 
-		result.n_cameras = 1;
+		result.n_cameras = 0;
 		result.n_frames = 1;
-		Mat &rgb = result.rgb_left.emplace_back().emplace_back();
-		Mat &depth = result.depth_left.emplace_back().emplace_back();
-		Mat &pose = result.extrinsic.emplace_back();
-		Camera &params = result.parameters.emplace_back();
+
+		std::map<string,int> cammap;
 
 		for (auto const& [path, data] : files_) {
 			if (path.rfind("-") == string::npos) {
@@ -471,6 +469,25 @@ Snapshot SnapshotReader::readArchive() {
 				continue;
 			}
 			string id = path.substr(0, path.find("-"));
+			int idx;
+
+			if (cammap.find(id) == cammap.end()) {
+				cammap[id] = result.n_cameras;
+				idx = result.n_cameras;
+				result.n_cameras++;
+
+				result.rgb_left.emplace_back().emplace_back();
+				result.depth_left.emplace_back().emplace_back();
+				result.extrinsic.emplace_back();
+				result.parameters.emplace_back();
+			} else {
+				idx = cammap[id];
+			}
+
+			Mat &rgb = result.rgb_left[idx][0];
+			Mat &depth = result.depth_left[idx][0];
+			Mat &pose = result.extrinsic[idx];
+			Camera &params = result.parameters[idx];
 
 			// TODO: verify that input is valid
 			// TODO: check that earlier results are not overwritten (status)