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to fix that I will use this outdated version.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;