Fix of bug - mistaken Nette\Http\Session for Nette\Http\SessionSection

In the last week the total rewrite broken the Gettext class, because the $this->container->session was replaced for $this->session which contains instance of Nette\Http\SessionSection and not Nette\Http\Session which which causes calling non impelented method isStarted on SessionSection instead of Session
(plus wrong variable annotain in the declaration)

I have fixed this by refactoring the name of the variable and creating new variable sessionSection, so the class now holds instance of Session and SessionSection