change google analytics interface

This is a related to my post at https://groups.google.com/forum/?fromgroups#!topic/gwt-platform/0cfnA9om3DM

It is a breaking change so needs thorough review before being accepted.

I removed the binding from default module since you now have to bind userAgent at the same time.  I think it might be good to add a separate analytics gin module so that analaytics, navigation tracker & UA can be installed all at once.

I moved the GAAccount annotation to the google analytics folder because I think it's a mistake to put all annotations in the same package just because they're annotations.  GAAccount.java is much more related to GoogleAnalytics.java than it is to DefaultPlace.java
I don't think you should add "final" in method.

I would like to hear what is your train of though for this.