wmaker: add workspace pager underlying configuration

This path is adding the functions and variables needed for workspace pager preferences.
An option to enable/disable the workspace pager, and one to set a default background image.

WindowMaker/Defaults/WindowMaker.in

@@ -3,6 +3,7 @@
   PopupSwitchMenu = NO;
   MenuStyle = normal;
   DisableMiniwindows = NO;
+  DisableWorkspacePager = NO;
   OpenTransientOnOwnerWorkspace = NO;
   EdgeResistance = 30;
   WorkspaceBorderSize = 0;