Remove panel title margin without body text

[colinrotherham]

This pull request patches the styling for govukPanel().

Currently:

1. The element govuk-panel__body { text } is optional
2. Margin is always applied to govuk-panel__title { titleText }

The title only needs a margin if the optional text is provided, otherwise vertical alignment is affected:

Once patched, the margin will be optional 👍

[kr8n3r]

Hi @colinrotherham

this looks like a good tweak. We just need a second confirmation from the team

[36degrees]

I'd like to make sure @dashouse has the chance to review this.

[dashouse]

👍
Thanks @colinrotherham