Wrong kernel started

I have a problem opening an .ipynb file.

In the ipynb file:

```
"metadata": {
"kernelspec": {
"display_name": "Python 2",
"language": "python",
"name": "python2"
},
```

`"jupyter kernelspec list"` gives:

```
freecad_kernel /home/gael/.local/share/jupyter/kernels/freecad_kernel
python2 /home/gael/.local/share/jupyter/kernels/python2
python3 /home/gael/.local/share/jupyter/kernels/python3
```

When I open the ipynb file, a FreeCAD window appears. This is the beginning of the log

```
NotebookEditor created for /home/gael/11-projects/2015-taros_demo/experiments/notebooks/test.ipynb
notebook-editor.js:258 kernelGateway.stderr [KernelGatewayApp] The Jupyter Kernel Gateway is running at: http://localhost:8892

notebook-editor.js:262 Kernel: freecad_kernel
notebook-editor.js:258 kernelGateway.stderr INFO:tornado.access:200 GET /api/kernelspecs?1458219661160 (127.0.0.1) 184.27ms
...
```

In the definition of freecad_kernel (`kernel.json`), I have `"language": "python"`.

The notebook was saved within the web browser launched from `jupyter-notebook`.

I would love to see atom-notebook running. It looks great and I don't like editing in the browser. Thanks for providing it! Thank you helping me solving this issue!

Start with the kernel-selection logic around the notebook-editor.js log, then compare the notebook's kernelspec metadata with the entries returned by `jupyter kernelspec list` and the shown freecad_kernel/kernel.json. Done means opening this notebook starts its Python 2 kernel rather than FreeCAD, with the selection behavior verified against this reproduction.

Written by the indexing model from the issue text.