Major config overhaul: use custom modules, setup for multi-host config, and less boilerplate

modules/themes/background-test.sh

@@ -0,0 +1,9 @@
+#!/bin/sh
+for i in $(ls -d */);
+do
+  if curl --output /dev/null --silent --head --fail $(cat $i/default.nix | grep "backgroundUrl" | cut -d'"' -f 2); then
+    echo "$i background successfully downloads";
+  else
+    echo -e "\033[0;31m$i background download fails\033[0m"
+fi
+done