Add a "fixed" cookie expiration date

[sly7-7]

Currently, if I understand well, the cookie expiration date is renewed every minutes if the page is visible. For my app, I would like the expiration date to be written only once when the user is authenticated. I don't find any public way to do that for now. What do you think about that ?

As a workaround, at the moment, I've overriden the private _isPageVisiblemethod in the cookie store to always return false.