GWT Implementation of GMaps Utility Library's Marker Manager

[Eric B]

Since the Google Maps API will soon be depreciating their own
implementation of MarkerManager in favor of the implementation in the
GMaps Utility Library project, I thought I'd jump the gun and
implement it in GWT, since that's the only way I use the Google Maps
API any more.

More details at http://www.ebessette.com/d/software/GWTMarkerManager.
I welcome any feedback.

Thanks,
Eric