Add npm linting/testing and build checks

• Check if npm run lint:js passes
• Check if `npm run test' passes
• Check if npm run build returns changed build files
• Cache node_modules

assigned to @ethitter

changed the description

mentioned in commit docker/images@ae71a659

mentioned in commit docker/images@6a628e33

mentioned in commit docker/images@115290c3

mentioned in commit docker/images@2bf2b1e8