Document how an Avatar can be removed from a vCard. Add a convenience method.

git-svn-id: http://svn.igniterealtime.org/svn/repos/smack/trunk@13583 b35dd754-fafc-0310-a699-88a17e54d16e
SMACK-413 fixed vCard parsing regarding the PHOTO element. Moved vCard test cases to unit-test where appropriate. Added testcases for vCard PHOTO parsing.

git-svn-id: http://svn.igniterealtime.org/svn/repos/smack/trunk@13584 b35dd754-fafc-0310-a699-88a17e54d16e