Fix GetChildElementById no access to elements inside Card

[jerone]

Pull request type

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• Bugfix
• New feature or enhancement
• UI change (please include screenshot!)
• Code style update (formatting, renaming)
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What is the current behavior?

Fixes: #1406

What is the new behavior?

• GetChildElementById now also iterates over UIElement inside UICard.

Other information

Added basic unit tests for GetChildElementById.

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[veler]

Hello,
Thank you for this fix! It looks great!