Implement field order for the action dynamic forms.

Perform action class validation by importing the class and
not relying on an instance of action model, which might not
exisit when still creating the action.

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

mayan/apps/document_states/classes.py

@@ -76,7 +76,12 @@ class WorkflowAction(six.with_metaclass(WorkflowActionMetaclass, WorkflowActionB
         self.form_data = form_data
 
     def get_form_schema(self, request=None):
-        return {
+        result = {
             'fields': self.fields or (),
             'widgets': getattr(self, 'widgets', {})
         }
+
+        if hasattr(self, 'field_order'):
+            result['field_order'] = self.field_order
+
+        return result