Remember selection "was employed" selection on Employment details

- Value of was employed is computed whether or not a employment
  relation exists on the claim. Unfortunately this means it's
  pre-selected as "No" the first time the user gets the page.
  We can revisit this later.
Merge pull request #253 from ministryofjustice/bug-fix/was-employed-selection-on-employment-form

Remember selection "was employed" selection on Employment details