Sam: Add exception handler for unstarted session. This is checked at the
beginning of GET/POST. In the future we could add condition() checks
to ensure that the user is allowed to be on the page. We could also
check if the user has provided the prerequisite data to even be
on the current page.
Merge branch 'master' of github.com:InsolvencyService/wader into session-error
Sam: Sanity check to see if the user has a session rather than showing 500.
Merge branch 'master' of github.com:InsolvencyService/wader into session-error
Merge pull request #286 from InsolvencyService/session-error

Session error