Having the hot corner activate the overview works rather poorly with scrolling
through the workspaces.
We disable the functionality by default. The preference `override-hot-corner`
controls the functionality, so set it to false if you want it back.
A possibility is having the hot-corner force the top bar to be visible when
a fullscreen window has focus, but it's not yet implemented.
We're assessing all top level declarations from outside the original scope when
we're evaluating code. So everything should be `var`.
Classes are `let` bound so we should use var for `ClickOverlay` too, but there's
a bug in gnome-shell-mode making such statements not evaluate. We therefor wait
for that to be fixed.
