Provisioning stanza XML schema almost complete

Most of the bare classes exist but functionality and documentation
needs to be written in. Then some unit testing for stanzas should be
done.
DownloadPrivilegesResponse add_privilege() working

I fixed it such that DownloadPrivilegesResponse is producing a correct
subelements of <include …/> and <exclude …/> for the DPR. Can only add
privileges you cannot remove them as of now.
canAccess Credentials Fixed

Discussed how credentials sub-element of canAccess is supposed to be.
There is a discrepancy in the spec how to properly do this. Talked with
Lance on what is more likely to be correct and decided to go with
<credentials type=“” value=“”>. He sent the XMPP board to make an
change to the spec.
Moved Credentials Class right above CanAccess

This is to make it easier to read and reference as coding and debugging
CanAccess class.
added skeleton methods to complete canAccess

canAccess has all necessary methods but needs to make them functional.