Parse form can break when no field type is passed.

[allanchau]

Describe the bug
When using multiple checkboxes in a custom form, this function will error with Expected field {field} is type of {field type}, but found type of {found field type}.

To Reproduce
Steps to reproduce the behavior:

1. Add multiple checkboxes to a custom form.
2. Post the form.

Expected behavior
The form should be parsed correctly.

Additional context
We need to update /Users/allanchau/Developer/idearium/linz/lib/api/formtools/parse-form.js to be a bit smarter and not just default to a string.