[BZ#693242] places-menu: Alphabetize the default places

Submitted by @jbicha

Description

gnome-shell 3.7.5 with gnome-shell-extensions 3.7.5 (jhbuild)

The places menu in GNOME Classic mode doesn't list the default places in alphabetical order (which also means that the list is in a different order than Nautilus. I'm attaching a simple patch which fixes this for English, but I guess the more complete patch would require sorting the localized list of default places (does Nautilus do this?)