Implement API key

[tucotuco]

Enable key= query parameter to identify source of request for statistical, not authentication purposes.

This will, more than anything, allow statistics on request coming from GEOLocate.

[tucotuco]

Authentication might need to happen (and probably through a more robust method that an API key) if feedback is going to be accepted. For example: authenticated clients could have the capability to request blocking a "bad" georeference in the gazetteer.