Allow superusers to change the Contributor of a Source

The ability to transfer the ownership of a "public list" to a contributor after
they sign up was lost when we transitioned to using the `Source` model and made
the `contributor` field read-only on the admin.

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 ### Changed
 - Replace facility history feature switch with feature flag [#881](https://github.com/open-apparel-registry/open-apparel-registry/pull/881)
 - Better accommodate outside contributors [#895](https://github.com/open-apparel-registry/open-apparel-registry/pull/895)
+- Allow superusers to change the Contributor of a Source [#901](https://github.com/open-apparel-registry/open-apparel-registry/pull/901)
 
 ### Deprecated
 

src/django/api/admin.py

@@ -108,7 +108,7 @@ class FacilityAliasAdmin(SimpleHistoryAdmin):
 
 
 class SourceAdmin(admin.ModelAdmin):
-    readonly_fields = ('contributor', 'source_type', 'facility_list', 'create')
+    readonly_fields = ('source_type', 'facility_list', 'create')
 
 
 admin_site.register(models.Version)