Problem: metadata mappings between ArchivesSpace and AM are hardcoded

[jhsimpson]

There is a workflow in Archivematica that integrates ArchivesSpace, Archivematica and DSpace (described here http://journal.code4lib.org/articles/12105)

In this workflow, when a user sends Transfers to backlog and then arranges those transfers into SIP's using the Appraisal Tab, metadata is collected from ArchivesSpace and then written to a dublin core dmdSec in the resulting AIP's METS file.

The metadata mapping used is buried in the code of Archivematica, and is not configurable by an end user, or even easily discoverable. The mapping should be configurable in some way by an enduser.

Here is where Archivematica pulls these fields from ArchivesSpace, to populate the dublin core dmdSec in the AIP's METS file:
https://github.com/artefactual/archivematica/blob/92d7abd238585e64e6064bc3f1ddfc663c4d3ace/src/dashboard/src/components/access/views.py#L420

A spreadsheet describing the current mappings used is here:
https://docs.google.com/spreadsheets/d/1wMi5nWakdREWsLFvqEPmGCRAeYAhbCQwrEBx3CcI6JU/edit?usp=sharing (relevant for #18 and #19 ).