I originally thought I would do this inside WindowServer, but let's try to
make it as a standalone app that communicates with WindowServer instead.
That will allow us to use LibGUI. :^)
When a mouse button is pressed inside a window, put that window into an
automatic mouse tracking state where all mouse events are sent to that
window until all mouse buttons are released.
This might feel even better if it only cared about the mouse buttons you
actually pressed while *inside* the windows to get released, I don't know.
I'll have to use it for a while and see how it's like.
