* Implemented XEP-0184 section 5.

* Added NS_RECEIPTS to protocol namespace list.
* Show our support of XEP-0184 in caps.
* Added a big, fat warning to get_contact as this does not work as
  expected.
* There was some strangeness in our XEP-0022, it added an id tag to
  the x tag, which isn't mentioned anywhere in the XEP. And for some
  strange reason, that id even was the same all the time.
* Fixed a typo.