With this patch the window manager related functionality is split out
onto a new endpoint pair named WindowManagerServer/Client. This allows
window manager functionality to be potentially privilege separated in
the future. To this end, a new client named WMConnectionClient
is used to maintain a window manager connection. When a process
connects to the endpoint and greets the WindowServer as a window manager
(via Window::make_window_manager(int)), they're subscribed to the events
they requested via the WM event mask.
This patch also removes the hardcoding of the Taskbar WindowType to
receive WM events automatically. However, being a window manager still
requires having an active window, at the moment.
