map landing page elements to Dublin Core using metatag

[ferrighi]

The following mapping is identified:
title->dcterms:title
field_abstract->dcterms:description
field_iso_topic_category->dcterms:subject
field_doi->dcterms:identifier
field_license->dcterms:rights

Additional static tags could be added:
dcterms:type-> "Dataset"

Additional tags could be extracted from MMD:
dataset_citation/dataset_publisher->dcterms:publisher

We have a problem with creators, as it is extracted as a text field containing not only names, but also emails and addresses