Added static attribute to polygon directive. Dramatically improves performance of polygons, especially those containing thousands of points. Setting the static attribute to true implies that both the polygon's points are static (do not change), and that the polygon is for display only (i.e. is not editable).  As a result, setting static to true overrides the editable attribute.  The performance benefit comes from the fact that the directive does not need to watch for edits from Google Maps, and does not need to perform deep watch on every polygon co-ordinate during every Angular digest cycle. (Although a watch is still performed on the path attribute for changes by reference so that the entire polygon can still be changed.)  On a map with multiple polygons with a total of 25,000+ coordinates, the browser would simply fail without the static atttribute, with the static attribute set to true the polygons are displayed almost instantly.