Refactor

- Form objects pass on all attributes to model
- Models delegate attributes to associated objects
  e.g. Claimant#address_post_code delegates to
  Address#post_code
- Deletes AttributeExtractor. No longer needed
- DRY up specs with shared examples
- Boolean writers no longer populate the attributes
  hash
- Boolean readers overridden with computed attributes
- Form attr_readers will look to its resource object
  for a value if there isn't one in the attributes hash.
  This will make forms work with the back button when its
  implemented