jskos-convert: table header aliases

[nichtich]

To align with https://github.com/n4o-rse/ta4-conservation-dev/issues/2 and similar tools:

• make parent an alias for broaderNotation
• allow syntax prefLabel_xx equivalent to prefLabel@xx

Tools differ still in whether and how they build URIs (from identifier, from notation, from label...), this cannot fully be unified.

[stefandesu]

Will be included in the next release.