Add resolved smart link API views. Add Smart link manager method

.get_for(document).

mayan/apps/linking/managers.py

@@ -0,0 +1,8 @@
+from django.db import models
+
+
+class SmartLinkManager(models.Manager):
+    def get_for(self, document):
+        return self.filter(
+            document_types=document.document_type, enabled=True
+        )