Review CSRF protection

[deviantony]

CSRF protection has been disabled in #310

The current implementation of CSRF cause issues when hosting multiple Portainer instances on the same host (multiple exposed ports for example).

Plus, this implementation does not have any token validity check and token expiration policy.

It also requires the CSRF data generated by the server to be persisted in order to restart/ugprade the portainer instance associated to a specified domain, otherwise users would need to clean out the cookies associated to the domain in order to retrieve a token valid with the new instance.

[deviantony]

Have a look at https://github.com/justinas/nosurf