Add `Content-Security-Policy` and `integrity` attributes to `<script>` tags

[nfreear]

...

• — securityHeaderMiddleware plugin;
• — Investigate other headers? helmentjs?

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• https://content-security-policy.com/examples/express-js/
• https://helmetjs.github.io/
• https://csp-evaluator.withgoogle.com/

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