Run EventBus on dedicated thread

[hinerm]

The DefaultEventBus is making poor choices in where to publish events.

• The immediate publish method publishes to the EDT. Thus if the result of this publish tries to do something on the EDT it will deadlock.
• The publishLater method uses ThreadService.run, which runs on an arbitrary thread. Thus subsequent publishLater calls are not guaranteed to execute in a consistent order.

To resolve this issue, we should have a dedicated SciJava event-processing thread which runs all EventBus publications.

[hinerm]

@ctrueden Did I get anything wrong here?

[ctrueden]

Looks good, I think.

[ctrueden]

The culprit is this line of code in the DefaultEventBus. The rationale for the change (6b878da41160da695f6552ee86f537cff2443faf) was performance, but unfortunately it comes at the expense of correctness. We will probably have to revert that commit to fix things.