Add support for IPv6

[Meisaka]

There is a whole wide world out there that uses the fancy "new" Internet protocol, version 6.
Eventually, there will come a time when Trillek will need to fully support it too

Currently, Trillek only explicitly supports IPv4 via the GUI, with access to name based lookup connections available via the "connect" command.
Although the client can technically resolve IPv6, the server currently does not allow listening on IPv6 sockets, so this feature can be considered incomplete, and as such, connecting to v6 addresses in the client has been temporarily disabled.

This is a reminder to improve client connection methods when the server supports for IPv6.