Add haskell-ide-engine to haskell layer

nixos/layers/dev-haskell.nix

 { pkgs, ... }:
 
+let
+  all-hies-repo = pkgs.fetchFromGitHub {
+    owner = "infinisil";
+    repo = "all-hies";
+    rev = "0cba12ce4df375766dd183b4beebdee7d8e36e12";
+    sha256 = "1f91nrksr2x0zi2kbsy6qf4fmb1ybpx9p55rijhhs05rssk4b0nq";
+  };
+  all-hies = import all-hies-repo {};
+
+in
 {
   environment.systemPackages = with pkgs; [
     stack
+    all-hies.latest
   ];
 }