change google analytics interface

Edit: wiki on how to use universal analytics:

https://github.com/ArcBees/GWTP/wiki/Universal-Analytics

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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

Edit: Breaking change is that the init method is removed, and googleanalytics is no longer bound by default module.  Also this code is completely untested.  I'm working on a new project which I'm only adding Universal Analytics to, so someone using the old version of analytics needs to test if everything still works.
There's already a Callback interface available in GWT or in GWTP