Increase group gap

[colin-grant-work]

What it does

Users have reported that the current gap between groups can be a bit small, especially when groups are large and / or there are many groups / row. This increases the gap between groups by another 2px.

Before:

After:

How to test

1. Confirm the slightly larger gap between groups.
2. Check that editing / line unbreakability is maintained with the new values.
3. Decide whether you like the bigger gap - it could be shifted to a preference, or left as is.

Review checklist

• as an author, I have thoroughly tested my changes and carefully followed the contribution guidelines

Reminder for reviewers

• as a reviewer, I agree to behave in accordance with the code of conduct

[arekzaluski]

LGTM