Chocolatey package: declare dependency on pslab-python #688

We have a Chocolatey package now thanks to tunisiano187. It is based on a nuspec file:
https://github.com/tunisiano187/Chocolatey-packages/blob/master/automatic/pslab-desktop/pslab-desktop.nuspec

However, for PSLab Desktop, you also need the Python library. So add another package for https://github.com/fossasia/pslab-python and declare it as a dependency. Then the installation on Windows should be more convenient.

Documentation on nuspec can be found here:
https://docs.microsoft.com/en-us/nuget/create-packages/creating-a-package