fixed crash in stanza_create_form when text is NULL

xmpp_stanza_get_text may return NULL.
Also fixed memory leak: xmpp_stanza_get_text returns new allocated
string and it must be freed by xmpp_free().
Added basic /rooms command to get chat room list
Page off after /rooms command
Added /disco command
Removed unnecessary NULL checks
Use domain part of current jid when no jid passed to /disco
Show name as well as jid for room list
Added output for /disco items
Implemented output for /disco info
Merge remote-tracking branch 'upstream/master'