sts based tracking

In my specific case, sig.length == 83, which does not decode properly with your decodeArray[83] list.
This pull request adds fingerprinting for a timestamp token present in the html and the com.google.youtube.util.SignatureDecipher class, which does the signature decoding in the flash player.

However, several Vevo videos I've checked use this same value, so I believe actually storing older values is not of any use in practice.