Changes date we get from pbcore to Date Portrayed from Asset Date.
Updates references in the code and fixes a test for the catalog show page. Fixes #579
Adds a trait to the pbcore_desc_doc factory and a test for date_portrayed
in the pbcore_desc_doc model
Merge pull request #616 from afred/use-date_portrayed-instead-of-assetdate

Use date portrayed instead of assetdate