Work towards #123 adaptive bitrate

Not complete but some useful changes to bitrate code so merged anyway. ABR disabled for now since it needs tuning and a better way of knowing when the bitrate change has actually taken effect.

components/common/cpp/include/ftl/timer.hpp

@@ -64,6 +64,8 @@ void setInterval(int ms);
 
 int getInterval();
 
+int64_t get_time();
+
 /**
  * Add the specified number of milliseconds to the clock when generating
  * timestamps. This is used to synchronise clocks on multiple machines as it