PR: Show kernel initialization errors in the IPython console

[ccordoba12]

Fixes #3458.

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This PR does several things:

1. Redirects the kernel process stderr output to a file and shows it in case of failure in our consoles. With this I'm trying to avoid the infinite stream of Kernel died, restarting messages and give feedback to users of what's the cause of the error.
2. Introduces a shortcut to restart kernels, so that we can override the one defined in qtconsole and control this process ourselves.
3. Clears the console on restarts.

[ccordoba12]

Ok, let's hope this one improves things for people with kernel problems :-)