Add hover effects to window controls

[Keith94]

Don't know if intentional or oversight, since hover color is not applied to window controls, but held color option is.

[Samillion]

It is intentional, yes. The held down effect is applied to all elements:

ModernZ/modernz.lua

Lines 999 to 1001 in 6c1b147

	if element.styledown then
	style_ass:append(osc_styles.element_down)
	end

Window controls have their own hover color effect just to differentiate. Which reminds me, someone requested that I should make the hover colors on window controls configurable. Not sure if I should add it or not. Hmmm.

[Keith94]

I kinda like uosc approach where there is a background hover effects applied to them as well.