Remove validation concerns from form objects

* Create separate validation objects for each document type.
* Convert ManualDocumentForm to a simpledelegator -- avoids unexpected
  errors where it doesn't proxy through methods as expected

+ @bestie
Rename form objects view adapters
Remove inheritance from CoreDocumentValidator
Merge pull request #173 from alphagov/create-validator-wrappers-which-arent-form-objects

Remove validation concerns from form objects