model-picker: can't define doubleClickItem

[Haz901]

Defining a doubleClickItem property in the options hash for a model-picker form field causes an error.

The form-field-options mixin tries to use defineProperty to define it, but that can only be done once, which means it breaks whenever any attribute changes (cannot redefine doubleClickItem on component)

Also, the function is never made into an action, which means it can't be called.