[#1389] Implement TrackEvent invariant. Close gh-260
[#1374] Constructor options are copied to a new object. Close gh-257
[#1384] Update plugin definition options in update.
[#1351] Implement TrackEvents methods: where(params), remove(params). Closes gh-224
[#1347] youtube wrapper to maintain its own current time, and do not bounce around during a seek.