User can edit/remove inventory count from any category

[armahillo]

From Rachel:

Must have a way to remove/adjust inventory count from any category! Sometime items get entered
incorrectly, not caught until later, then needs to be removed from inventory.

The big concern, for data integrity, is that there is some kind of audit record for the change.

There are a few different ways this could be approached -- if it were possible to adjust the erroneous donation, (via Donation#Edit) then the existing audit trail is preserved, although I suspect that this will not address all possible cases (maybe they do an inventory count and notice discrepancies but don't know if it's inventory shrinkage or a typo in the intake).

Another possibility is to create an Adjustment model to track these inventory changes. The quantities are changed directly in the inventories themselves, but there is a record on file (with comment) indicating the change. This could then be included in reports so that the totals add up correctly.

ie, for Item X:
(Donation total: 110) + (Adjustment total: -10) - (Distribution total: 50) = (Inventory total: 50)