Reduce the usage of lodash

[SukkaW]

html-webpack-plugin supports Node.js 10.13.0 and above which has full ES2018 support. We should prefer the ECMAScript built-in features (i.e. replace lodash/uniq w/ Set, replace lodash/extend w/ Object.assign). And instead of requiring a full lodash package, we can just use lodash.template to support the template.