Ci/linting

[AlexKMarshall]

This sets up linting on the React side. Mainly following information from https://www.robertcooper.me/using-eslint-and-prettier-in-a-typescript-project and facebook/create-react-app#8849

Add the following to your VSCode settings.json file to automatically apply linter fixes when you save files

{
  "editor.codeActionsOnSave": {
    "source.fixAll.eslint": true
  },
}

Note that the .env file for the client side is committed to the repo as described at https://create-react-app.dev/docs/adding-custom-environment-variables/

Secret variables must not be added to this file, as they will be visible in the final build of the client.

This PR also adds a pre-commit hook to run the linter. It will fix automatically any files it can, but anything that it can't fix automatically will cause the commit to fail until you fix them manually.

[codecov-commenter]

Codecov Report

Merging #8 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master      #8   +/-   ##
======================================
  Coverage    2.27%   2.27%           
======================================
  Files           3       3           
  Lines          44      44           
  Branches       12      12           
======================================
  Hits            1       1           
  Misses         43      43           

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[AlexKMarshall]

This is replaced by #16