Add <daogrp> to EAD export, fixes #2589

Squashed commit of the following:

commit f40a001566570e326915bcc1eb68b389e1d2cc84
Author: José Raddaoui Marín <raddaouimarin@gmail.com>
Date:   Wed Feb 20 04:09:51 2013 +0100

    Change href value in daoloc for external digital objects

commit fef85bf9abd879410716190a375ee40c89581110
Author: José Raddaoui Marín <raddaouimarin@gmail.com>
Date:   Wed Feb 20 03:39:33 2013 +0100

    Add mimeType and id to <daoloc> in EAD export

commit deb395d31635dcb57d38443e221abd089ae6c1d1
Author: José Raddaoui Marín <raddaouimarin@gmail.com>
Date:   Wed Feb 20 02:55:51 2013 +0100

    Add <daogrp> to EAD export