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/include/ftl/timer.hpp

@@ -23,6 +23,19 @@ enum timerlevel_t {
 	kTimerMAXLEVEL
 };
 
+/**
+ * Represents a timer job for control purposes. Use to remove timer jobs in
+ * a destructor, for example.
+ */
+struct TimerHandle {
+	const int id = -1;
+
+	void cancel() const;
+	void pause() const;
+	void unpause() const;
+	TimerHandle &operator=(const TimerHandle &h) { const_cast<int&>(id) = h.id; return *this; }
+};
+
 /**
  * Milliseconds between calls.
  */
@@ -44,13 +57,7 @@ void setClockAdjustment(int64_t ms);
  * If all high precision callbacks together take more than 1ms to complete, a
  * warning is produced.
  */
-int add(timerlevel_t, const std::function<void(int64_t ts)> &);
-
-
-/**
- * Remove a callback using an ID returned when it was added.
- */
-void remove(int);
+const TimerHandle add(timerlevel_t, const std::function<void(int64_t ts)> &);
 
 /**
  * Initiate the timer and optionally block the current process.