Use airbnb-eslint config

[tejasbubane]

From #645

Turn on airbnb-base for maintaining via a script that switches this.

In a later change, we should turn on several rules that guard against potential bugs, such as no-shadow, no-undefined, no-var; additionally we can add stylistic consistency without forcing style choises such as consistent spacing (but not required).

We should stay with eslint:recommended for exercises (end users) and use airbnb only for this repo. @SleeplessByte

Wait for #680 to be merged so that we can exclude airbnb from package.json checksum CI task.

[SleeplessByte]

Yes yes yes! This is exactly what I meant.