Fixed a typo in checkCollisionsOnProposedTranslations, but I think this function can be way simplified.
Found out through testing that PiecewiseCurve.evaluateCrossings probably doesn't work, but I'm going to ignore that for now and make IntroSimulation.checkCollisionsOnProposedTranslation use rectangle collision detection instead of piecewise curves because the function already assumes rectangular shapes, and this makes it simpler and requires a whole lot less overhead.