Linting

[Iain-S]

I ran ESLint demo on the JS:

• There are other things we could do to it if we wanted to move to the ES6 standard (e.g. use let or const in place of var)

I ran flake8 on the .py files:

• There are a number of unused variables in lab_black.py, which we should probably use or delete
• Other than the unused variables, there are no flake8 errors
• I created a black_formatter variable in nb_black because it doesn't need to be shared with lab_black and it was causing an unused variable error