Quick fix for decimal serialisation bug in form.
Quick fix for decimal serialisation bug in form.

Simply cast a decimal field as a string.
Not doing more or fiddling with the tests (coverage is poor!) as
Rebecca is in here also cleaning up the tests.

LandRegistry/casework-frontend-alpha,LandRegistry/casework-frontend-alpha,LandRegistry/casework-frontend-alpha,LandRegistry/casework-frontend-alpha