fix/215: Render the express payment button in the editor

[Sidsector9]

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• Does your code follow the WooCommerce Sniffs variant of WordPress coding standards?
• Have you written new tests for your changes, as applicable?
• Have you successfully run tests with your changes locally?
• Will this change require new documentation or changes to existing documentation?

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Changes proposed in this Pull Request:

Closes #215

Steps to test the changes in this Pull Request:

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