Add "Active" column to discount codes table
Created by: seancolsen
This makes it easier to manage discount codes when you have a whole lot of them and many of them are disabled.
- Active discount codes are visually indistinguishable from inactive ones.
- There is no way to view a list of all active discount codes.
- A new column shows the status of each code.
- Users can sort by this column to show only the active codes.
Fixes #182 (closed)