In-app barcode scanning

[erickok]

The Barcode Scanner dependency app for barcode scanning was simple to integrate and its nice we need to permission, but forcing to install it is a bit clumsy and some users despise it (arguably for good reason).

Find an alternative app or, more likely, make the barcode scanning in-app using Vision APIs (perhaps https://github.com/nisrulz/qreader). We likely need the camera permission anyway for #20.