Differentiate consumables that can be self checkout

[htmr80]

Features

• Add a new flag in Consumable “allow_self_checkout”
  • Default value: True
• In /consumables
  • When user is not a member of staff
  • Filter the list of consumables to only display the ones that have flag allow_self_checkout set to True
  • Prevent the user from checking out a consumable that does not have a allow_self_checkout set to True
• All consumables can be checked out through the post usage questions
• Display the number of supplies left (quantity) near the consumable name (only non-reusable)
  • (sold-out) indicator when 0 left
  • Remove + button when 0 left (sold out)

Tests

• Check that POST /consumable prevents the user from checking out consumables that have allow_self_checkout set to False