Automatically run IPython magic commands at loading

[stevenlis]

I send a feature request https://github.com/microsoft/vscode-python/issues/6344 to display the plots in the interactive window as PNGs.

@rchiodo suggested to run the following command:

%config InlineBackend.figure_format = 'png'

While waiting for the request to be implemented, I have to copy it to every single python file of mine. It would be much more convenient if vscode could run it for me automatically whenever the python extension is loaded.

There might be many magic commands a user would like to run based on their preference. I believe adding such a function would be very useful.

[greazer]

Let's add a setting that accepts a set of python statements as a single string.

[DavidKutu]

Ready for the next release.

[DavidKutu]

The setting will be called 'Run Startup Commands'