Timestamp is part of the client id

Working on an implementation that uses the _ga client id and passing to the measurement protocol api I noticed that the timestamp is part of the client. This seems to be confirmed by a Google employee in the following thread: https://groups.google.com/forum/#!topic/google-analytics-analyticsjs/AUc1LonR-6c

This is a BC break so I tagged current state of master to 0.1.0.

@ricbra @eriwin 
Oke clear.