Update PMD4 validations to reflect current muttnik expectations (#1249)

[kieranlives]

• [x] Change DatasetExactlyOneContents -> DatasetMaxOneContents
• [x] Change DatasetExactlyOneGraph -> DatasetMinOneGraph
• [x] Remove DatasetExactlyOneLabel
• [x] Add DatasetExactlyOneTitle
• [x] Remove DatasetMaxOneContributor
• [x] Remove RecordExactlyOneLabel
• [x] Individual tests for modified/new validations
• [x] Run PMD4 suite on removed validations

Run tests with clojure -M:test

[kieranlives]

Er, I meant to write https://github.com/Swirrl/muttnik/pull/1327#issuecomment-937678328 on this PR!

[RickMoynihan]

@Robsteranium I've been through each of these and they seem good. And I've updated @kieranlives corresponding muttnik PR so it now passes wrt IC-19.

https://github.com/Swirrl/muttnik/pull/1327

This means once that PR is merged, muttnik fixtures will be aligned with these changes.

Are there any other comments on these changes?

[Robsteranium]

I've merged this in to #24.

Thanks!