[#1] Handle spatial field, test for frequency

The base euro profile will only store the spatial uri in the
`spatial_uri` extra (you are supposed to use a controlled vocabulary).

Frequency also uses a controlled vocabulary.
[#1] Parse publisher fields

Added a helper function to parse fields from foaf:Agent based entities.
Fields checked are name, email, url, type and uri. On the CKAN dataset
these get created as `dcat_publisher_*`
[#1] Store contact details (just name and email for now)
[#1] Don't prefix DCAT extras with `dcat_`

To improve clarity and interoperatibility.

There is a compatibility mode though that can be set to true (via the
ckanext.dcat.compatibility_mode config option) to maintain the fields
returned by the current version of the ckanext-dcat.

Changes are
* issued, modified, publisher_name, publisher_email prefixed by dcat_
* language is a comma separated string instead of a dump of JSON list
Merge branch 'master' of github.com:okfn/ckanext-sweden