Meta issue: Security improvement

[ShGKme]

Checklist:

• [x] Remove SameSite=Lax -> SameSite=None cookies patching (fixed in: https://github.com/nextcloud/talk-desktop/pull/22)
• [x] ~~#18~~
• [ ] Follow Electron / Best Practices / Security
  • [x] 1. Only load secure content
  • [x] 2. Do not enable Node.js integration for remote content
  • [x] 3. Enable Context Isolation
  • [x] 4. Enable process sandboxing
  • [ ] 5. Handle session permission requests from remote content
  • [x] 6. Do not disable webSecurity (https://github.com/nextcloud/talk-desktop/pull/22)
  • [ ] 7. Define a Content Security Policy
  • [x] 8. Do not enable allowRunningInsecureContent
  • [x] 9. Do not enable experimental features
  • [x] 10. Do not use enableBlinkFeatures
  • [x] 11. Do not use allowpopups for WebViews
  • [x] 12. Verify WebView options before creation
  • [x] 13. Disable or limit navigation
  • [x] 14. Disable or limit creation of new windows
  • [ ] 15. Do not use shell.openExternal with untrusted content
  • [x] 16. Use a current version of Electron
  • [ ] 17. Validate the sender of all IPC messages
  • [x] 18. Avoid usage of the file:// protocol and prefer usage of custom protocols (https://github.com/nextcloud/talk-desktop/pull/1204)
  • [ ] 19. Check which fuses you can change
  • [x] 20. Do not expose Electron APIs to untrusted web content