Harden http request and response

[johanjanssens]

Prevent direct access to the data in the request object by enforcing that the ->get($var, $filter) is used. Trying to direct access data should thrown an exception.

• https://www.keycdn.com/support/http-strict-transport-security
• https://scotthelme.co.uk/hpkp-http-public-key-pinning/
• https://www.keycdn.com/blog/http-security-headers
• https://www.keycdn.com/support/content-security-policy