Add option to disable images in browse.kml.php 

This adds an option to disable images in the item-bubble/KML file. 

I have a project where we'll be populating a large map with a few hundred items and would like to keep the size of that request as small as possible.

_(This project will ultimately entail disabling/bypassing the MAX_LOCATIONS_PER_PAGE settings, but that's another issue – one that I haven't really looked at yet)_