Add support to update the document indexes from workflow state changes.

Add a new workflow field called internal_name for easier workflow
reference in document index templates.
Generalize the PropertyHelper class.

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

mayan/apps/document_states/tasks.py

@@ -18,7 +18,7 @@ def task_launch_all_workflows():
 
     logger.info('Start launching workflows')
     for document in Document.objects.all():
-        print 'document :', document
+        logger.debug('Lauching workflows for document ID: %d', document.pk)
         Workflow.objects.launch_for(document=document)
 
     logger.info('Finished launching workflows')