Update TaskOrderForm so that it converts empty string for number into None, this was causing an issue where new TOs were being saved with an empty string for the number, which violated the unique constraint.
TOs.
The enum for the CLIN type needs to be coerced in the form data so that
the `jedi_clin_field` data is the value of the enum option. Perviously
the `jedi_clin_field` was being populated with a stringified
representation of the enum, like `JEDICLINType.JEDI_CLIN_1`.