data: set shell classic mode via env variable instead of command line

Currently, we start gnome-shell in classic mode by passing
--mode=classic to the gnome-shell command line. This --mode=classic
gets stripped away when the session is saved, which breaks classic
mode on subsequent login attempts.

This commit changes the session file to set the
GNOME_SHELL_SESSION_MODE environment variable instead.

https://bugzilla.gnome.org/show_bug.cgi?id=720894
window-list: remove our use of Hash module

It was removed in core shell and replaced with ES6 Map.
Bump version to 3.11.4

To go along GNOME Shell 3.11.4