Remove all references to use-x-times and free-shipping for coupons.

These seem to be legacy references from before 3.8. No need to replicate
these features when the underlying database structure isn't there.
Use plus / minus buttons to add / remove coupon conditions. The condition fields
are also now translatable properly.
Coupon statuses are displayed as text rather than icons.
Adjust coupon condition field's width.
Fix: Adding conditions when editing coupon doesn't work.
Update messages for coupon
CSS style for datepicker
Checkbox labels should be next to the checkboxes themselves.
Fix bugs with coupon start & expiration timezone.

- Timezones are not taken into account
- Can't save start / expire time when editing coupon.