Improve clarity of product availability in CP order edit page

[jmauzyk]

What are you trying to do?
It would be helpful to give a little more detail regarding product availability when selecting line items in the CP order edit page. This way admins would be able to discern between products that are discontinued and no longer for sale and those that are still active but just temporarily out of stock.

What's your proposed solution?
Ideally, I think there would be column for Stock in addition to Available? and these would match the pattern in CP product indexes: Available? would display a check mark to convey its Available for purchase status, and Stock would display ∞ for unlimited qty, a number for specific qtys, and blank for no stock. To save space, this could all be condensed into the Available? column, but I think that might be a bit less clear.