CSP is used to avoid some attacks where the hacker tries to execute
untrusted code in the browser.
The policy is to use assets hosted on the the original website and in order to make CSP work with material UI, a nonce is generated at each request of index.html and injected in the template as well as provided in the Content-Security-Policy header (https://material-ui.com/styles/advanced/#how-does-one-implement-csp)
Fix#815
