Make Geonames API key a variable during installation

the current default uses Reinier's api key. This key by default should be filled in by the user during installation

The help text should explain that she can create a username here

http://www.geonames.org/login

And (copied from http://www.geonames.org/export/web-services.html )

"The username for your application can be registered here. You will then receive an email with a confirmation link and after you have confirmed the email you can enable your account for the webservice on your account page"

The strongarm setting needs to be removed from features as well.

And finally, we should create a new username on geonode, called devtracdemo that we will set as default (with all sorts of warnings about that it is shared, and might stop working!)