Make thumbnails in design lists not distorted

What does this MR do?

Prevents the thumbnails from being distorted.

It maintains a 230px height on the "canvas" to fill with the image, but doesn't stretch the actual image.

Double checked on Edge 15.

Before this MR (master)	After this MR

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

IE11 has an unrelated problem.