Allow bypassing CSRf protection by settng res.bypassCsrf true.

Note: I am re-opening this PR now that it is based against development branch.

Motivation: sometimes it is necessary to disable CSRF on some routes or based on some other criteria - for example, whether the requesting client/browser actually supports sessions.

My use-case is that I need to bypass CSRF whenever someone has authenticated with an API key using HTTP Basic Auth and is connecting using cURL or similar means where sessions do not exist or are cumbersome to setup for an API consumer.

Note: it is true that if my API consumer were to connect using a regular browser, it would make the app possibly vulnerable to CSRF attacks (because HTTP Auth headers are cached by browsers). However, I believe it is a concern that the app developer has to take care of by explaining the implications to API consumers. Maybe it is also worth noting that I have looked at several SaaS APIs that use HTTP Basic Auth for authentication and do not have any kind of CSRF protection in place.