XEP-0077 Added Functionality

Created XMPPRegistration to handle the cancellation of an existing registration ([XEP-0077 3.2](http://xmpp.org/extensions/xep-0077.html#usecases-cancel)) and changing a user's password ([XEP-0077 3.3](http://xmpp.org/extensions/xep-0077.html#usecases-changepw)).