Added the ability to pass a function into pileup click handler

[denisemauldin]

@akmorrow13 I can't tell how to get the click test to work.

drawnObjectsWith(testDiv, '.pileup') throws a failure even though if I comment out the other tests and remove the resets on testDiv and p, it displays fine in the browser.

There seems to be a timing issue because sometimes var canvasList = testDiv.getElementsByTagName('canvas'); has two elements and sometimes it doesn't. Maybe hasPileupSelector is not an appropriate wait for this test?

I don't know how to get what offset I should provide to the ReactTestUtils.Simulate.click.

Thanks for your help.

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This change is 

[akmorrow13]

@denisemauldin you can run the tests interactively by running the http server and going to test-runner (instructions here).

npm run http-server
open http://localhost:8080/src/test/runner.html

I am not sure if you already tried this but it can help debug the ordering of events.

[denisemauldin]

@akmorrow13 Yeah, that's what I've been doing - http://localhost:8080/src/test/runner.html?grep=FeatureTrack

If I comment out all of the other tests, the p.destroy(), and the testDiv.innerHTML = ''; in the afterEach then it shows the pileup on the screen, but the canvas variable is still undefined.