Improved event tracking

[kirlat]

This is an implementation of @irina060981 suggestion: alpheios-project/components#308 (comment)

We already have a PsEventData object that contains a caller's class name. So the only addition required is the name of the caller function. I added this as a second argument to the pub() method. That's optional and can be omitted. This way we can use without the second argument it if a caller name tracking is not required and for compatibility with the existing code.

PsEventData object is passed to the callback function as a second argument, right after data. That would allow to use it as an optional arguments: callbacks that do not need this info can ignore it, others can use it.

I've also added a description getter that outputs event tracking information in a "human-readable form" of:
LexicalQuery.finalize -> [Lexical Query Complete]
(what was the caller and what was an event name)

Please let me know what do you think. Just want to offer this for discussion. I thought it would be easier to submit a PR than to describe everything in an issue. Thanks!

P.S. For alpheios-project/components#308

[balmas]

Looks good to me once the tests are fixed and updated :-)

[irina060981]

I like it :)

[kirlat]

@irina060981 This has been merged into master, so we can start using the improved tracking functionality