autoload googleearth and kml

this is a response to #509 

now, when loading a new kml, if GoogleEarth is not running/initialized, the kml string is stored, then, when GoogleEarth is activated, the kml string list is parsed and the kml loaded into GoogleEarth.

I have also added an option to autoload GoogleEarth when a kml is loaded.

I have moved the GoogleEarth load and unload code out of the button/toggle action, to be able to call GoogleEarth load code from the addKml plugin.

can be tested there http://preprod.cartoriviera.ch/och/wsgi/