Add blur and make dotfiles more flexible

Add blur using the fork from https://github.com/tryone144/compton.
picom seems to be very CPU heavy on my system, so until I figure out how
to fix that I will use this outdated version.
Make the dotfiles a bit more flexible by creating symlinks for stuff
like the wallpaper or the compositor. When switching/exchanging these
components only the symlinks have to be updated.

.config/compton/compton.conf

@@ -0,0 +1,4 @@
+backend = "glx";
+blur-method = "kawase";
+blur-strength = 6;
+blur-background = true;

.config/compton/launch.sh

@@ -0,0 +1,7 @@
+#!/bin/sh
+
+if [ "$1" = "-k" ];  then
+	killall -q compton
+elif ! pgrep -ax compton >/dev/null 2>&1; then
+	compton --config "${XDG_CONFIG_HOME:-$HOME/.config}/compton/compton.conf" -b
+fi