[vector-api] Change default anchor for KML icons from Google Maps

This PR is potentially contentious.

The [KML specification of IconStyle](https://developers.google.com/kml/documentation/kmlreference#iconstyle) does not clearly specify a default hotSpot (anchor). Many KML files use icons from Google Maps, and from [looking at them](http://ex-ample.blogspot.fr/2011/08/all-url-of-markers-used-by-google-maps.html) it seems that the default anchor is [16, 32]. This PR includes a hack to override the anchors of such markers.

Before:
![before](https://f.cloud.github.com/assets/6942/1859673/75aefc08-77a7-11e3-8ffc-c7d700737162.png)

After:
![after](https://f.cloud.github.com/assets/6942/1859684/9f02ec18-77a7-11e3-8983-fbc8b1539019.png)

cc @oterral