compositor: Switch from compton to picom

Switch to ibhagwan's picom fork with dual_kawase blur and rounded
corners.

.config/picom/launch.sh

@@ -0,0 +1,10 @@
+#!/bin/sh
+
+basedir="$(cd "$(dirname "$0")" && pwd -P)"
+compositor="$(basename "$basedir")"
+
+if [ "$1" = "-k" ];  then
+	killall -q "$compositor"
+elif ! pgrep -ax "$compositor" >/dev/null 2>&1; then
+	"$compositor" --config "$basedir/$compositor".conf -b
+fi