This also has the added benefit that after a restart we don't get the
same random numbers all the time because we forgot to initialize the
RNG with srand().
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. :^)
This matches basically all other Spider implementations I've played,
and makes playing much easier :)
I have left click-to-reveal in place, but mostly incase there is a
condition I've forgotten about.
Scoring is designed to mimic Microsoft's implementation - starting at
500, decreasing by 1 every move, and increasing by 100 for every full
stack.
Fixes GH-5319.
