zipcode lookup now needs api key

[RussH]

The zipcode lookup now needs an API key. Individual instances will have to request an api key and amend the ziplookup URL (in /lib/ziplookup.php) to use their individual API key. Free lookups up to a $200 monthly limit.

REQUEST_DENIED You must use an API key to authenticate each request to Google Maps Platform APIs. For additional information, please refer to http://g.co/dev/maps-no-account

[RussH]

URL format to be: https://maps.googleapis.com/maps/api/geocode/xml?key=ABC123YOURKEYGOESHEREABC123&sensor=false&address=

[RussH]

I'll port this to the wiki