Improve GeoIP diagnostics #3458

To help make it easier to figure out when GeoIP isn't setup correctly, we should display more information.

• For the PECL extension & PHP API, display the available database types (ie, country or city or whatever).
• For the Apache extension, display the available server variables.
• If the Apache extension is not installed, display list of installed modules (result of apache_get_modules()). If function not available, say assuming non-apache web server because it isn't available.
• For the PECL extension, display the value of geoip.custom_directory or if not set.
• Make sure DataTable footer message for Region + City reports only show if region/city information is available.

see also #3442

(In [7469]) Fixes #3458, fixes #3515, improved geoip diagnostics/help & allowed IPv4-mapped IP addresses to be geo-located.