Add fields to api content type

[timwood]

Proposed Fields

Name (dcterms:title)
Description (dcterms:description)
URL to Documentation (dcat:dataDictionary)
Service Endpoint URL (dcat:WebService)
Tags (dcat:keyword)
Agency (datagov:Agency)

Primary fields (the MVAP -- minimum viable API profile)
Summary
Category
Tags
Description
API Home Page
Logo

Fields discussed here: http://wiki.data.gov/wiki/Draft_API_Catalog_metadata_schema