Merge branch 'metadata-admin-raw' into 'master'

Prevent thousands of SQL queries in MetaData admin

Closes #800

See merge request !1421

arkindex/documents/admin.py

@@ -76,7 +76,7 @@ class MetaDataAdmin(admin.ModelAdmin):
     list_display = ('id', 'name', 'type', )
     list_filter = [('type', EnumFieldListFilter), ]
     readonly_fields = ('id', )
-    raw_id_fields = ('element', 'entity', )
+    raw_id_fields = ('element', 'entity', 'worker_version')
 
 
 class MetaDataInline(admin.TabularInline):