Fix some issues affecting compositor usage

[WillPower3309]

A few points from the scenefx patch notes on dwl:

NOTE: Some GTK apps are being cut off when they have shadows enabled. You can use the shadow_ignore_list option to prevent shadows from being rendered on those apps

NOTE: Blur doesn't work on windows with opacity set (opacity_active, opacity_inactive)

NOTE: In DWL's Makefile scenefx must be placed before wlroots, e.g. PKGS = scenefx wlroots wayland-server ...