Allow users to decide if they want to stay signed in on this device

[aeneasr]

"Keep me signed in on this device" tells the browser (when using the session issuer) to set a TTL on the browser cookie (e.g. 90 days). If the browser's cookie policy allows remembering cookies in such a way, the user will have his session for that period of time and will have to log in again once the TTL expires.

As an alternative, the TTL is not sent, telling the browser to delete the cookie when closing the window (or the browser, depends on the implementation).

The difficulty is adding this to the form field during sign in and combining that with the session hook.

Another question is how this should be handled for Social Providers.

Another question is how this should be dealt with after registration.