Ref: https://valadoc.org/gtk+-3.0/Gtk.Widget.margin_left.html
Ref: https://valadoc.org/gtk+-3.0/Gtk.Widget.margin_right.html

Ref: https://valadoc.org/posix/Posix.SIGTERM.html

We only care whether the background is stretched across multiple monitors
or not, let's be explicit and make it clear.

Session is more used

* Cleand up and fixed compiler warnings.

* Update menubar.vala

Removed commented code.

* Update slick-greeter.vala