Add IDN support to proxy error pages

[zzz]

All code currently in SusiDNS AddressBean?. Move to net.i2p.util for access by i2ptunnel, check and convert all hostnames.

Low priority, the only IDN hostnames we have registered now are just for testing.

After this, there are lots of forms throughout the console and webapps for entering or displaying hostnames. Even lower priority.