Applications previously had to create a GUI::Menubar object, add menus
to it, and then call GUI::Window::set_menubar().
This patch introduces GUI::Window::add_menu() which creates the menubar
automatically and adds items to it. Application code becomes slightly
simpler as a result. :^)
Since applications using Core::EventLoop no longer need to create a
socket in /tmp/rpc/, and also don't need to listen for incoming
connections on this socket, we can remove a whole bunch of pledges!
Instead of having the window non-resizable, it now defaults to a frame
size of 200 x 200 pixels but is user-resizable. The shown screenshot
updates its size accordingly. :^)
Sometimes we might need a larger view, or a non-square shape.
