Synchronize the bulk coupon generation form with the single coupon add form

These two forms are misaligned. For starters, the labels for coupon usage limits are different in each form. They should be the same.

More importantly, it is not possible to set a start date (or optional end date) on the bulk generation form. Instead, bulk generated coupons use the request time as the start date. I can't think of any reason we should support these on the single form and not bulk generation - guessing it was a feature that was added after the bulk generation form was created and it just didn't make its way into that form.