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/forms.py

@@ -8,7 +8,7 @@ from .models import Workflow, WorkflowState, WorkflowTransition
 
 class WorkflowForm(forms.ModelForm):
     class Meta:
-        fields = ('label',)
+        fields = ('label', 'internal_name')
         model = Workflow