$domain defaults, domain wildcard support

Patch:

optional $domain param: defaults to 'localhost' or $_SERVER['HTTP_HOST']

Previously, you would need to code around keys_api_get_key($service, $domain) and check the host to provide the proper domain. Now keys_api_get_key is smart enough to get the proper $domain default.

support for .example.com domain wildcards

Rather than entering multiple keys for related domains, support .example.com wildcard. Previously, you would need to enter the same key for:

www.example.com
beta.example.com
dev.example.com

...etc

clean up error message

Proper t() usage, and adds manage key link only if authorized to use it