By arjenk: Fixed dc.date field, type is char, not date.

According to Dublin Core the dc:date field is less restricting than the
current implementation datetime. This converts the tpe to string. See
http://dublincore.org/documents/dcmi-terms/#terms-date for more
information.
By arjenk: Added drush mm-meta-copy and mm-meta-update. Added 2 new drush functions to manipulate metadata of lots of assets in 1 run.
Version 3.5.1-dev build 2088.