Feature: Barrier Events

[nathanwbrei]

This PR brings back barrier events definitively. Barrier events have come and gone in various forms, but hopefully this is their final form. This PR also adds a new tool for visualizing how threads are utilized, including exact event assignments and barrier events.

It also bundles in a couple of bugfixes:

• JEventSource::FinishEvent() was being called spuriously when a JEventSourceArrow returned an (unused) JEvent to the pool after the JEventSource rejected it with FailureTryAgain
• There was a data race in the new JLogger timestamps because, curiously, std::localtime is not threadsafe (!)
• When populating the JParameterManager at startup, JFactory::DoInit() was silently swallowing an exception due to a null JApplication pointer.