Add multiple claimants to the flow (WIP)

- [x] Add multiple claimants to the flow
- [x] Hypenate URLs #296 
- [x] Non-JS solution to non-destructively add claimants
- [x] i18n
- [ ] Styling
- [ ] Progressive reveal
- [x] Destruction of arbitrary claimants
This is a full test for the additional claimants page covering all the actions because we don't add additional claimants in the generic create claims feature. This is because there is no way to indicate remissions for multiple claimants currently.

I'm probably going to go back through our feature specs and do a comprehensive spec like this for each form page.