[core_pyside2] startup fix

[kay-jahnke]

Description

Actually starting the modules listed under "startup" in the config.

Motivation and Context

The startup parameter was loaded in the config, but the modules were not started.

How Has This Been Tested?

Tested with custom config on Windows 10 21H1 for the following cases:

• missing startup
• empty startup
• valid startup
• startup with incorrect module name

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• [x] My code follows the code style of this project.
• [ ] I have documented my changes in the changelog (documentation/changelog.md)
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have added/updated for the module the config example in the docstring of the class accordingly.
• [x] I have checked that the change does not contain obvious errors (syntax, indentation, mutable default values).
• [x] I have tested my changes using 'Load all modules' on the default dummy configuration with my changes included.
• [ ] All changed Jupyter notebooks have been stripped of their output cells.

[Neverhorst]

I mean in principle the code looks good. I'm unable to test it right now with an actual setup. However, I'm a bit concerned about loading a huge number of complex modules before starting the Qt event loop. It's probably irrelevant but one should test this with complex modules to be sure.

[kay-jahnke]

I actually had already though about the starting of the modules before the event loop, but I did not find a better place for it. Is there a hook which we could use that let's us start it after the event loop?