Introduce panel window list

[Scott Moreau]

This patch series implements several new features for the shell. The focus is
a window list for the panel. There are a decent amount of protocol additions
required but fortunately most of them are local weston desktop-shell protocol.
The wayland protcol patch is needed for 5/7 on.

A few new paths are opened here which means an opportunity for bugs. I did
notice that clients may crash if they do not support the new wayland protocol.
Also, desktop-shell is prone to crash because of the bug fixed by these patches
http://lists.freedesktop.org/archives/wayland-devel/2012-October/006021.html and
http://lists.freedesktop.org/archives/wayland-devel/2012-October/006022.html
The functionality of the window list works fairly well overall from my tests.


Features provided by this patch set:

* Panel window list complete with drag-n-drop to reorder items
* Minimize implementation; hook up client minimize button
* Right-click-drop-down-menu with Minimize, Maximize and Close


Other thoughts:

The fallback cairo icon is used for debugging and demonstration. Clients need
to start using wl_shell_surface_set_class() so the compositor can discover its
.desktop file and subsequently, an icon. The titlebar right-click menu should
probably have similar items as the panel window list item right click menu.