[baker] show less options in coupon dropdown fields

[bbelderbos]

forms.py queryset override:

• coupon recipient field needs to hide baker user
• coupon treat field needs to hide treat request

-- need to find resource ...

[bbelderbos]

@adamdoty here you go ...

You can override the queryset on a field, example: https://stackoverflow.com/a/27914030

[adamdoty]

took a little tweaking from the post, but got it