Sorting of IDN domains

[edmondas]

This is related to #475

When opening the "List zones" overview (list_zones.php) and sorting by "Name", all IDN domains are at the bottom, because the sorting doesn't match on the unicode version of the domain name, but on the punycode - which also means that all domains are collected under the letter x, because the punycode starts with "xn--".

It's quite complicated because you'd have to store the domain somewhere in utf8 form to use for sql sorting, or you'd have to rethink the whole mechanism. This involves natural sorting as well, and there is another issue with reverse records, so it's not so easy.