Update devtools to enable strict mode via query param

[camdecoster]

Description

Update plotly.js DevTools to enable strict mode (used for content security policy testing) via query param.

Screenshots

Before	After

Testing

• Start the server in normal mode with this command: npm start
• Open the Network tab of the browser DevTools and reload the page
• Note that no CSP header is returned in the response of the initial request
• Close the server
• Start the server using strict mode with this command: npm run strict
• Open the Network tab of the browser DevTools and reload the page
• Note that a CSP header is returned in the response of the initial request

Notes

• The policies enabled for this mode include the following:
  script-src 'self'; style-src 'self' 'unsafe-inline'; worker-src blob:
• One can turn on strict mode by adding the query param 'strict' with any truthy value
• When in strict mode, the page title includes the word 'strict' and the words 'STRICT MODE' are added to the header bar