Use . notation for ng-model to allow nested models

The model for a form currently has to be completely flat i.e. every
field must be an attribute of the form's `ngModel`. Forms cannot
"reach into" subattributes because the lookup is via a single key.
Fix this limitation by using a dot notation instead.
Pretty sure this should still be option.val, typos on the following line (all my fault) notwithstanding.