AnglePlay.findResponses() uses PFUtil.findEvents()

The new function is an optimized re-write of the
old p2mFindEvents function
AnglePlay.explainableVariance() created

* Replaces findExplainableVariance() method
* Collapses across stroke before comparing responses
* Prevents under-estimation of explainable variance
for AnglePlay caused by RasterUtil.explainableVariance()
AnglePlay.predictionScoresOverTime() actually computes prediction scores

* before it showed explained variance over time but now it divides by explainable variance to get a prediction score.
AnglePlay.predictionScoresOverTime() demo added