wmaker: add core workspace pager functions

This patch is adding the core code needed to run the workspace pager.

Currently when called, a new frame presenting mini workspace images
are displayed at the bottom of the screen above other windows.
When clicking on one of the miniatures, the workspace is switched and
the frame is closed.

Drawbacks: a screenshot of the workspace is used for the miniatures.
This screenshot is taken only when a workspace switched event occurs.

First, it means that the workspace switching process can be longer than
usual. Secondly, updated minitatures can only be available when the
workspace is "opened" (cause windows have to be mapped to be able to
be copied).

So when wmaker is (re)started or when for example a window is moved to
another workspace the corresponding miniature is NOT updated.
(I did not find a clean and easy way to do so, feel free to share if
you have some ideas)

src/wsmap.h

@@ -0,0 +1,28 @@
+/*
+ *  Window Maker window manager
+ *
+ *  Copyright (c) 2014 Window Maker Team
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License along
+ *  with this program, see the file COPYING.
+ */
+
+#ifndef WSMAP_H
+#define WSMAP_H
+
+Bool process_workspacemap_event;
+
+void wWorkspaceMapUpdate(WScreen *scr);
+void StartWorkspaceMap(WScreen *scr);
+
+#endif