[#64] Show relevant Additional Info

Updated the harvester extension point to pick up the necessary fields.
Topic category facet will stop working.
[#21] Make topic-category multivalue

Custom field in the Solr schema to make the topic-category field
multivalued, otherwise it only came up once on datasets with multiple
categories. A bit of fiddling with the extra value required (needed to
dump as JSON string)
[#23] Create organizations from harvested metadata

Assign datasets to an organization matching the ISO ResponsibleParty,
creating it if needed. We extract the organization title (used to create
a URL friendly name), and url and email if present, which are stored as
extras.
Merge branch 'master' of github.com:okfn/ckanext-tsbsatellites