Minor improvements to relation badges on user profiles

What does this PR do?

This PR makes a few minor improvements to the "relation" badges that display on another user's profile.

• Use semantic HTML to improve screen reader support.
• Add "Mutuals" and "Following" badges to go with "Follows you". Only one of these will be shown at a time.
• Add "Blocking you" badge that is displayed to moderators only.

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