Allow the 'Origin' field on a custom fermentable to be null

[Kevin The Stout]

Currently, when adding a custom fermentable to the inventory you're forced to select a value for the 'Origin' field from a menu of about a dozen countries. This value is then added to the name of the custom fermentable when it's used in a recipe. The appearance of the recipe would be tidier if the country of origin information could be (optionally) omitted.