Plugin to query Cisco directory

I use Jitsi at work, where we are in the process of moving from Cisco phones to SIP. Unfortunately our internal extension numbers are not available in our LDAP server. I saw SIP has a presence protocol, but it does not seem to work with our configuration.

Anyway, to make the transition easier I wrote a external contact source that queries the Cisco IP Phone directory. Typically this is an URL like `http://SERVER:8080/ccmcip/xmldirectorylist.jsp`. It returns a XML document listing pairs of name and phone numbers ([documented here](http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cuipph/all_models/xsi/9_1_1/CUIP_BK_P82B3B16_00_phones-services-application-development-notes/CUIP_BK_P82B3B16_00_phones-services-application-development-notes_chapter_011.html#CUIP_RF_C09FE419_00)).

I tried to stick to the Jitsi coding style and standard.
Let me know if you think this can be included or if I'm completely misled ;)