chore: Significantly restructure folder layout

This moves the various projects from "type-based" folders (such as
"services" or "tools") into more appropriate semantic folders (such as
"nix", "ops" or "web").

Deprecated projects (nixcon-demo & gotest) which only existed for
testing/demonstration purposes have been removed.

(Note: *all* builds are broken with this commit)

ops/sync-gcsr/default.nix

@@ -0,0 +1,10 @@
+{ pkgs, ... }:
+
+pkgs.buildGo.program {
+  name = "sync-gcsr";
+  srcs = [ ./main.go ];
+
+  deps = with pkgs.third_party; map (p: p.gopkg) [
+    gopkgs."gopkg.in".src-d.go-git
+  ];
+}