Added support for HOXT (XEP-0332)

This is initial impementation of XEP-0332 (SMACK-552) -
HTTP over XMPP transport.
Created extensions, providers and unit tests.
Two features are missing: jingle and sipub.
Merge pull request #3 from Tsyko/xep-0332

Initial implementation of "HTTP over XMPP transport" (XEP-0332)