Buggy Store Merch Editing Interface

[farisashai]

Lots of fun bugs to fix 😃

Steps to reproduce:

• View merch store as an admin

• Click the edit button on an item

• Try to file upload a new image
  - Bug: Upload freezes and does not let you change the image.
  

• Try to delete file upload.
  - Bug: Page crashes and goes blank.

• Refresh page
  - Bug: Collection Name field displays the wrong value
  

• Try to add variants to an existing item
  - Bug: Disabled unless we completely delete the item and create a new one

• Apply a 100% discount code.
  - Bug: Allows the discount code to be applied in the editing item UI and backend but doesn't actually do anything. (Disable this value if it's not allowed)
• 
  

UI Nitpick:
I'm not a big fan of this quantity adjustment field as a way of changing the quantity.

We should either be able to directly enter the quantity we want to set the item to or maybe have "+" and "-" increment buttons to the side of the quantity field to manually adjust the value and save it