uxmpp library and demo changes

Hey, Devi.
I have changed the demo and library a little.
Added in uxmpp.pas 
TPresenceEvent, TIqVcardEvent procedures,
FOnPresence, FOnIqVcard fields,
OnPreserce, OnIqVcard properties,
updated
TXmpp.ParsingIQ and TXmpp.ParsingPresence functions,

changes in dpr:
converted with Lazarus to Lazarus project.
added cthreads in case of Linux and FreePascal

changes in mainunit:
added handlers for VCard and Presence, illustrated how do they work.

changes in interface:
added username and
password fields which will allow to not hardcode them in the source.