replace accession csv fixture with random data
revise accession converter test and add test for processing date
add processing_started_date field to collection_management
add processing_started_date mapping to accession converter
revise digital_object converter spec
add processing_started_date mapping to digital_object converter
Add migration to add processing_started_date to collection management records
Merge pull request #636 from hudmol/pr-634

Pr 634