leksah: move to haskell tools and add cabal to path

pkgs/development/tools/haskell/leksah/default.nix

@@ -0,0 +1,17 @@
+{ stdenv, ghcWithPackages, gtk3, makeWrapper }:
+
+let
+leksahEnv = ghcWithPackages (self: [ self.leksah-server self.leksah self.cabal-install ]);
+in stdenv.mkDerivation {
+  name = "leksah";
+
+  buildInputs = [ gtk3 ];
+  nativeBuildInputs = [ makeWrapper ];
+
+  buildCommand = ''
+    mkdir -p $out/bin
+    makeWrapper ${leksahEnv}/bin/leksah $out/bin/leksah \
+      --prefix PATH : "${leksahEnv}/bin" \
+      --prefix XDG_DATA_DIRS : "$GSETTINGS_SCHEMAS_PATH"
+  '';
+}