Spyder fails to create kernel.json files if jupyter_runtime_dir is not writable

[ccordoba12]

This error was reported here:

http://stackoverflow.com/q/40643760/438386

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Solution: If jupyter_runtime_dir is not writable we need to switch to TEMPDIR (defined in utils/programs) to save and load kernel.json files.

@mariacamilaremolinagutierrez, I'm assigning this one to you because you also have issue #3630.

[ccordoba12]

Scratch my previous solution! Using a different directory other than jupyter_runtime_dir would impose a great burden on us.

So what we need to do is:

1. Prevent Spyder from crashing when jupyter_runtime_dir is not writable.
2. Show an error message in our IPython consoles warning users that they need to make jupyter_runtime_dir writable in order for Spyder to create consoles for them.

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@mariacamilaremolinagutierrez, about showing errors please see the method called create_new_client in plugins/ipythonconsole.py