qOverload is used to disambiguate pointers to overloaded functions, but
most of the usages in the code base were with non-overloaded functions.

GraphicsInteger is used by the panes in the Graphics config window to
create spin boxes that change their associated config setting, and
update their own state when something else changes the config setting.

Despite its current name nothing about this class is particular to the
Graphics window, so renaming it to ConfigInteger better reflects its
purpose. This should also make it less confusing when ConfigIntegers
are added to other config windows.