This patch begins the transition away from the global menu towards
per-window menus instead.
The global menu looks neat, but has always felt clunky, and there
are a number of usability problems with it, especially in programs
with multiple windows.
You can now call GUI::Window::set_menubar() to add a menubar to
your window. It will be specific to that one window only.
Minimum window size can now be customised and set at runtime via the
SetWindowMinimumSize WindowServer message and the set_minimum_size
LibGUI::Window method. The default minimum size remains at 50x50.
Some behind-the-scenes mechanics had to be added to LibGUI::Window to
ensure that the minimum size is remembered if set before the window is
shown. WindowServer sends a resize event to the client if it requests a
size on create that's smaller than it's minimum size.
The WM_* IPC messages are intended for "outsider" window management,
not for a client's own windows. Make a separate StartWindowResize
message for this.
This was the only reason that every IPC client had to know its server
side client ID.
Adds a mechanism through which windowing clients can re-request an
UpdateSystemTheme message. This is currently used in SystemMenu's
ShutdownDialog to refresh it's theme when the dialog is instantiated.
Instead of storing the back/front buffers of a GUI::Window as just
Gfx::Bitmap, wrap them in a WindowBackingStore class.
This will allow us to add more information alongside the bitmaps while
keeping the back/front swapping logic simple.
