Update PlantUML Maven Plugin and drop requirement for dot

[mthmulders]

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Closes #630.

[kwin]

any reason this is not affected by the global pragma?

[mthmulders]

No clue. Trial and error showed me that the nested diagram needs this separately. Also happened when I had the diagram open in VS Code, so it seems to me it's not a Maven plugin issue.

[mthmulders]

Closed in 10d086a.