Ability to set nickname to join the chat

Current muc join dialog only accepts jid and pw (and autojoin toggle) but not nick. The nick is then derived from the account:

        handle = g_hash_table_lookup(data, "handle");
...
        if(!handle)
                handle = js->user->node;

thus could be sent as "handle" element in the components table.

P.S. I've tried to edit dialog ui with glade but it doesn't work :(