Add initial definition file for google.visualization.

This definition file is incomplete. I wrote it because I was using
google's GeoChart in a typescript file, and needed the definitions. It
contains google.load and google.setOnLoadCallback, the visualization
module, one (overloaded) event, and interfaces for the GeoChart. It also
contains an arrayToDataTable function definition. More to come as I
expand upon this definition file locally.