Add IPv6 support

At some point, IPv6 support should be added.

On the database level, this requires converting all given IPv4 INET values to IPv6 INET values, since IPv4 and IPv6 values do not play nicely together in PostgreSQL <= 8.4.8. (see: http://archives.postgresql.org/pgsql-admin/2011-07/msg00201.php) A helpful postgres dev suggests doing something along the lines of the following:

"address = '::ffff:0.0.0.0'::inet + (NEW.address::varchar::inet - '0.0.0.0'::inet)"

Next, statusapp.views.helpers.is_ipaddress and statusapp.views.helpers.is_ip_in_subnet should be rewritten to work with both IPv4 and IPv6 input and IP addresses.