More Feedback from CMS Form Processor

The CMS section editor form now gives more relevant feedback to the user
after processing. The results page now tells the user if the save succeeded
or if there was an error.

Basically, the BaseSection model raises an Exception when our conditions
are not met. The relevant view (ContentManagement.py) function catches
that Exception and return the message for the template to render. On the
shell, the user will simply see the Exception as is.

More later.