In a previous commit, we start/stop these timers based on number of
ports tracking stream stats triggered by RPCs. However, timers cannot
be triggered across threads (RPC thread and main thread in this case).
This fix uses a queued connection to post it to the other queue.
The stream timingHash is read by getStreamStats() while it is read/write
for processRecords(), the latter is a more frequent operation so there's
no real benefit of using a read-write lock instead of simple mutex.
This singleton class will keep track of Ttag timing across all ports and GUIDs.
A bunch of FIXMEs/TODOs are pending for this class implementation; also this
class has not been hooked up to the rest of the code yet.
