Change urls

Closes #245 

Application number is now back in the form flow `/apply/application_number`

User session controller handles returning(`/application/returning`) and reminding(`/application/reminder`) users

```ruby
if claim && claim.authenticate password
  errors.add(:password, I18n.t('errors.user_session.invalid'))
else
  errors.add(:reference, I18n.t('errors.user_session.not_found'))
end
```
or 

```ruby
if claim.try :authenticate, password
  errors.add(:password, I18n.t('errors.user_session.invalid'))
else
  errors.add(:reference, I18n.t('errors.user_session.not_found'))
end
```

are better, no?