display: Optionally sort window list

https://bugzilla.gnome.org/show_bug.cgi?id=737581
workspace: Correctly initialize MRU list

The workspace MRU lists are updated when windows are managed/unmanaged
or change workspaces. However those updates obviously only apply to
existing workspaces - new workspaces will always start out with an empty
MRU list, despite sticky windows already being "on" that workspace.
As we now assert that the list contains all windows located on the
workspace, we need to initialize it correctly to avoid a crash.

https://bugzilla.gnome.org/show_bug.cgi?id=737581