pythonPackages.moviepy: Add optional deps

Don't include them by default because they increase the derivation size
from ~200M to over 600M.

pkgs/development/python-modules/moviepy/default.nix

@@ -10,8 +10,20 @@
 , proglog
 , requests
 , tqdm
+# Advanced image processing (triples size of output)
+, advancedProcessing ? false
+, opencv ? null
+, scikitimage ? null
+, scikitlearn ? null
+, scipy ? null
+, matplotlib ? null
+, youtube-dl ? null
 }:
 
+assert advancedProcessing -> (
+  opencv != null && scikitimage != null && scikitlearn != null
+  && scipy != null && matplotlib != null && youtube-dl != null);
+
 buildPythonPackage rec {
   pname = "moviepy";
   version = "1.0.0";
@@ -23,9 +35,14 @@ buildPythonPackage rec {
     sha256 = "16c7ffca23d90c76dd7b163f648c8166dfd589b7c180b8ff75aa327ae0a2fc6d";
   };
 
-  # No tests
+  # No tests, require network connection
   doCheck = false;
-  propagatedBuildInputs = [ numpy decorator imageio imageio-ffmpeg tqdm requests proglog ];
+
+  propagatedBuildInputs = [
+    numpy decorator imageio imageio-ffmpeg tqdm requests proglog
+  ] ++ (stdenv.lib.optionals advancedProcessing [
+    opencv scikitimage scikitlearn scipy matplotlib youtube-dl
+  ]);
 
   meta = with stdenv.lib; {
     description = "Video editing with Python";