QR code improvements

- Display QR codes as links to served images
- The qr_code plugin caches these images in the background
- Make a qr_code template to push out as a modal form
- Create a QRCodeView to simplify display of QR codes
- Add option to launchModalForm() to disable the 'submit' button

Refactored QR code display for

- StockLocation
- StockItem
- Part

InvenTree/part/models.py

@@ -180,7 +180,6 @@ class Part(models.Model):
     def __str__(self):
         return "{n} - {d}".format(n=self.name, d=self.description)
 
-    @property
     def format_barcode(self):
         """ Return a JSON string for formatting a barcode for this Part object """