polybar: Make hardcoded paths dependant from XDG

Instead of hardcoding the paths of all the scripts, use env variables
that are set in launch.sh. This way the config also works with
XDG_CONFIG_HOME not set to ~/.config.
Sadly polybar only accepts references that stand on their own.
(So something like ${env:XDG_CONFIG_HOME:~/.config}/polybar/<script>
does not work.) Hence the mess with the associative array and the
variables for every module.

.config/polybar/scripts/vpn.sh

@@ -0,0 +1,17 @@
+#!/bin/sh
+
+connection="$(nmcli con show --active | awk '$3 ~ /^(vpn|tun)$/ { print $1 }')"
+if [ -n "$connection" ]; then
+    echo "VPN: $connection"
+    exit 0
+fi
+
+# [o] is a hack to not grep the grep-command
+# see: https://stackoverflow.com/questions/9375711/more-elegant-ps-aux-grep-v-grep
+if ps ax | grep -q "[o]penvpn"; then
+	echo "VPN"
+	exit 0
+fi
+
+echo
+exit 1