stockpile: add a minimum of zero; editing amount of an item

[aixtools]

Sometimes I just want to know how much stock I have, as an inventory, without any specific minimum.

a) make a minimum of zero possible

b) and when a minimum does become necessary - would be much nicer if when I select edit it defaults to the amount, rather than the item-type. imho, the number/amount needed is more likely to change, than the type.