Added subject and classification functionality.

Hi,

It's not much, but I've added a little bit of functionality for the subjects and classifications rake tasks (as well as some documentation).

We've started to play around with creating workflows for our own subjects and found them useful - would like to know what you think!

Thanks, Tom
Instead of iterating over these you can use destroy_all on the collection (ie Classification.destroy_all) This should be faster than destroying each record separately