Related links on service page should require link text or present the url as link

[finnlewis]

Steps to demonstrate odd behaviour:

1. Edit a service page
2. Add a related link
3. Do not give the link any link text
4. Save
5. See a related links block with no link.

6. Edit again
7. Add Link Text
8. Save
9. See the link

So we either want to

a. make the link text required
b. set the theme to render the link text if present, or just the url as link text if nor.

@markconroy @andybroomfield @ekes which is the best balance of better and quick?

[markconroy]

My preference would be to make the link text required.