Don't set global jupyter_notebook_config.py file

This is picked up by the dev instance of JupyterLab as well,
possibly leading to infinite recursion

binder/postBuild

@@ -1,4 +1,2 @@
 pip install -e .
-jlpm build
-mkdir -p ${NB_PYTHON_PREFIX}/etc/jupyter
-cp binder/jupyter_notebook_config.py ${NB_PYTHON_PREFIX}/etc/jupyter
+jlpm build

binder/start

@@ -0,0 +1,9 @@
+#!/usr/bin/env python3
+import sys
+import shutil
+import os
+
+argv = sys.argv[1:] + ['--config', 'binder/jupyter_notebook_config.py']
+print(argv)
+
+os.execv(shutil.which(argv[0]), argv)