Refactor the document metadata add, edit and remove views.

mayan/apps/metadata/managers.py

@@ -1,6 +1,22 @@
+from __future__ import unicode_literals
+
 from django.db import models
 
 
 class MetadataTypeManager(models.Manager):
     def get_by_natural_key(self, name):
         return self.get(name=name)
+
+    def get_for_document(self, document):
+        return self.filter(
+            pk__in=document.metadata.values_list(
+                'metadata_type', flat=True
+            )
+        )
+
+    def get_for_document_type(self, document_type):
+        return self.filter(
+            pk__in=document_type.metadata.values_list(
+                'metadata_type', flat=True
+            )
+        )