Update documentation for Replaces and isReplacedBy

[karenmajewicz]

The metadata fields Replaces and isReplacedBy can indicate a relationship between two records A and B where:

• A= old data, deprecated but still available
• B= new data, to be used instead of A

For the purposes of GeoBlacklight, users only need to enter a value (ID of corresponding record) in the field Replaces in record B. This is because GeoBlacklight is set up to create widgets that display a two-way relationship that has only been declared on one record. (see the Data Relations documentation for more details)

For the purposes of OpenGeoMetadata, users should enter a value (ID of corresponding record) in both records. This is to ensure that the relationship is declared in the metadata regardless of how a discovery application functions.

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Furthermore, we should note that is would be a Best Practice to also include a warning in the displayNote field to alert users to deprecated datasets.

[rmseifried]

We'll probably want to update the documentation on the new Relations Fields page as well.