ChronometricAge updates to existing classes/terms

[essvee]

See review session notes from 19th Jan, 2023 and 13th Apr

• [x] Add note to class-level term that if you don’t have a range of chronometric ages in your collection (just a single one) you should set the value of ‘earliest//latest’ to be the same. A single chronometric age follows dwc and both earliest and latest should be the same value.
• [x] Add class-level note along the lines of 'Whilst dwc ChronometricAge class allows you to mix chronoage and chromostrat we recommend that you do not do that for LtC. You should use this class only when you have carried out analysis that produces a result and can hopefully document the method/protocol/technique (either as a reference or a text string description).'
• [x] ChronometricAge.verbatimChronometricAge: remove stratigraphically pre-1104 from examples.
• [x] ChronometricAge.chronometricAgeProtocol: update examples with the meteoritic ones Ben is going to provide.
• [ ] In light of the previous points, the skos mapping for this class and any updated terms will need to be checked - looks like some of them are down as exactMatch for dwc equivalent?

... these might need to be broken down into individual issues when we're finished with the review, but as they're all relatively minor modifications I figured they could share an issue for now.

[essvee]

See #445 for chronometricAgeProtocol examples.

[essvee]

Closed by #480 - skos mappings need to be re-checked as a whole so that can be a separate issue to deal with later.