*Nothing is wired up yet, this is just a displayable applet initially hardcoded to 4 workspaces. That will change to the actual number of workspaces once this is wired up to wayfire

A previous overzealous cleanup left some hanging screen variables and
one instance of an uninitialized screen being used.

Recent versions of libwnck introduced a WnckHandler object to be used as
the main entry point into the library.

There are no distros (that I could find) that ship both an old
libwnck<3.32.0 with a new MATE>=1.28. Dropping this should be safe and
removes complexity.

Since all of these were already wrapped inside HAVE_X11, it should not
affect Wayland at all.

Screen functions are replaced with their Display equivalents to remove
deprecation warnings. Display functions take into account the entire
display server connection, rather than a single physical monitor.

Since the icon loader is no longer present, there is no need to track
the icon theme when the applet is realized. This is will all be taken
care of by libwnck.

This function only loads the icon during the startup-notification, at
which point it gets replaced by the actual icon read in libwnck. Moving
forward the loading function should become part of libwnck.