Add focuslist

[Josef-Thorne-A]

Adds the focuslist package.

Checklist:

• Meaningful commit message, eg add my-cool-package (please not mention build-constraints.yml)

• At least 30 minutes have passed since uploading to Hackage

• On your own machine, in a new directory, you have successfully run the following set of commands (replace $package with the name of the package that is submitted, and $version with the version of the package you want to get into Stackage):

  stack unpack $package-$version
  cd $package-$version
  stack init --resolver nightly
  stack build --resolver nightly --haddock --test --bench --no-run-benchmarks