Use resource params for state transitions

Moves params used for control flow between form states into the resource params,
e.g. params[:was_employed] becomes params[:respondent][:was_employed] with this
commit. This commit also stores these things in the DB because the user can go
back and forth arbitrarily between states, we need to know their value if a
user revisits a particular state so we can show the page how they left it. In
future we can probably be smarter about these attributes by computing them from
other attributes but this is fine for now.
Remove redundant radio disclosure view helper
Merge pull request #2 from ministryofjustice/bye-virtual-attributes

Use resource params for state transitions
Add the wonderful stylings and scriptures of one Fazell "@demwunz" Williams
Styling

- simple_form config to add expected classes
- Massage the claimant form to pick up some styles
GDS dates

- Custom simple_form input type for GDS style dates, e.g. f.input as: :gds_date
- As the user can now easily submit arbitrary characters, handle argument error
  from a date failing to parse.
- Update forms and feature specs with GDS style date inputs
Input styling

- Style date inputs per GDS standard
- Style form inputs

Radio styling is broken. Next commit will fix.
Rename GDS date to "know date"

This morning @matharden told me this is the actual name of the pattern.
Fix radio button styling
Merges front-end CSS and adds hints

- Adds and correctly display hint
- Adds hint strings to i18n locale