Add run.py script to jsmodules/webpack-config (#1243)

This is intended to replace simpler uses of .npm_run_helper.py, then
    I'll continually migrate views until they can use the simpler form.
    Currently it will only be Splore that uses it.

jsmodules/webpack-config/run.py

@@ -0,0 +1,23 @@
+#!/usr/bin/env python
+
+import argparse, os, subprocess, sys
+
+def main():
+    parser = argparse.ArgumentParser()
+    parser.add_argument('--out', type=str, help='destination js file')
+    parser.add_argument('--src', type=str, help='source of main js file')
+    parser.add_argument('mode', type=str, help='"production" or "development"')
+    args = parser.parse_args()
+
+    env = {
+        'NODE_ENV': args.mode,
+        'BABEL_ENV': args.mode,
+    }.update(os.environ)
+    subprocess.check_call(
+            ['node_modules/.bin/webpack',
+                '--config', 'node_modules/@attic/webpack-config/index.js', args.src, args.out],
+            env=env, shell=False)
+
+
+if __name__ == "__main__":
+    main()