Fixed ImageSliderWidget update when the startpage was updated

[fkloes]

Description

This ticket is about to fix and issue with the ImageSliderWidget which didn't update properly, when the related page config was updated.
This issue caused broken images on a persisted startpage, when the image URLs where outdated.

Type of change

• 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)
• Polish 💅 (Just some cleanups)
• Docs 📝 (Changes in the documentations)
• Internal 🏠 Only relates to internal processes.

How to test it

• configure an ImageSliderWidget on your startpage with at least two images
• open the PWA startpage
• change the configuration / order of the widget
• reload the PWA startpage
  The startpage should reflect the updated widget configuration after the getPageConfig for the startpage came in.

[coveralls]

Pull Request Test Coverage Report for Build 1937

• 0 of 1 (0.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.003%) to 46.847%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
themes/theme-ios11/pages/Product/components/AddToCartBar/components/CartItemsCount/style.js	0	1	0.0%

Totals
Change from base Build 1936:	-0.003%
Covered Lines:	4954
Relevant Lines:	9911

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💛 - Coveralls