[Feature Request] Allow custom number for removing/replacing items

[RiderExMachina]

Preferably with a digital 10-key, but might get away with just a textbox.

Will be complete when it's possible to add/remove N qty from any item.

[RiderExMachina]

Steps to complete

• [x] Pressing button brings up "custom entry" textbox
  • [x] Textbox effectively has a digital 10-key
• [x] Pressing Enter or similar updates the quantity
• [x] Page automatically refreshes to reflect update
• [x] Custom entry textbox shows up for any item
• [ ] Custom entry textbox disappears if "cancel" is pressed