add modules.nix

Importing modules.nix enables the stand-alone use of the modules, without the
config presets of nix-bitcoin.nix.

modules/modules.nix

@@ -0,0 +1,31 @@
+{ config, pkgs, ... }:
+let
+  nixpkgs-pinned = import ../pkgs/nixpkgs-pinned.nix;
+  unstable = import nixpkgs-pinned.nixpkgs-unstable {};
+
+  allPackages = pkgs: (import ../pkgs { inherit pkgs; }) // {
+    bitcoin = unstable.bitcoin.override { miniupnpc = null; };
+    bitcoind = unstable.bitcoind.override { miniupnpc = null; };
+    clightning = unstable.clightning;
+    lnd = unstable.lnd;
+  };
+in {
+  imports = [
+    ./bitcoind.nix
+    ./clightning.nix
+    ./lightning-charge.nix
+    ./nanopos.nix
+    ./nix-bitcoin-webindex.nix
+    ./liquid.nix
+    ./spark-wallet.nix
+    ./electrs.nix
+    ./onion-chef.nix
+    ./recurring-donations.nix
+    ./hardware-wallets.nix
+    ./lnd.nix
+  ];
+
+  disabledModules = [ "services/networking/bitcoind.nix" ];
+
+  nixpkgs.overlays = [ (self: super: allPackages super) ];
+}