[PRIORITY] Session optimization

[AlexTr]

Now session cookie expiration date is renewed upon each page access, as the result 'set-cookie' header is send with each page response.
The possible fixes would be
a) if remember me is set, then set cookie for a month or so and don't update expiration time
b) if remember me is set, then set cookie for 50years expiration date, then track real cookie expiration date in session DB table