[#1709] Add resource extras to Solr index

Added multivalued dynamicField to Solr schema.
Used this: 
[http://ckan.readthedocs.org/en/latest/maintaining/configuration.html#ckan-extra-resource-fields](http://ckan.readthedocs.org/en/latest/maintaining/configuration.html#ckan-extra-resource-fields) 
to determine which fields to index.