Add scroll-factor Window Rule

[bbb651]

Example window rule:

window-rule {
	match app-id=r#"^wev$"#
	scroll-factor 4
}

Note this multiples the scroll factor rather than override it like the issue suggested. This way you can normalize all the window scroll factors once, and it'll scale like you'd expect when changing your input scroll factor and when using multiple input devices with different scroll factors. You can "reset" a scroll factor by setting it to the input device's scroll factor inverse.

Fixes #909.

[YaLTeR]

Otherwise looks good

[YaLTeR]

Rebased and made it work in popups too.

[YaLTeR]

Thanks. Guess it would make sense to add as a layer rule too