To progressively achieve the sidelist, let's start by moving
the current iconview selector to the side and then turning
it into a GtkListBox.
This commit, then, moves the iconviews' list to the start of
the horizontal box added in the previous commit.
https://bugzilla.gnome.org/show_bug.cgi?id=766922
The copied files are exact copies of shell/cc-window.c and
shell/cc-window.h, and they'll be used to implement the restyled
shell as an alternative binary.
https://bugzilla.gnome.org/show_bug.cgi?id=766922