* fix(backend): set http security headers (vol.1)
* (vol.2) minimal *working* content security policy
* (vol.3) set csp only if https and if hosted on cloud
* improve generics
* get CLOUD_HOSTED from extension
* remove X-XSS-Protection
rationale as per: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-XSS-Protection
* conditionally set all security related http headers