Refactor widgets creation, add smaller methods

[mmalczak]

ARTIQ Pull Request

Description of Changes

Create experiment widgets in separate methods.

Related Issue

Type of Changes

	Type
✓	🔨 Refactoring

Steps (Choose relevant, delete irrelevant before submitting)

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Licensing

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[SimonRenblad]

Instead of separate functions for each type of setting, perhaps separate out the scheduler settings as a whole and leave the bottom two buttons as is? This would probably help simplify logic in #2724. I don't think "having smaller methods" on it's own is a sufficient reason to move things around.