[RCD] IDNA support

I'm preparing for implementing IDNA support. I need to make a decission about the format used for storing IDN domains/addresses in database. UTF8 or Punnycode?

For contacts it's obvious that we should store them in utf8, because of contacts searching. But it's not so obvious for users/identities tables. Some (many) mail backends are storing IDN in punnycode format. So, if you have some integration scripts that are working on Roundcube together with those backends DBs it would be simpler to have punnycode in Roundcube too. What do you think?