review controlled list "relationType"

to be discussed in CCT1: review controlled list of relationType

• whether to reduce controlled lists of relationType to only active / only passive?
• be consistent
• add "descriptions" to schema spec. document, see also descriptions in exact matches here

also see #43

assigned to @markus.kubin

mentioned in merge request !8

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mentioned in issue #34

mentioned in issue #43

changed the description

assigned to @markus-kubin and unassigned @markus.kubin

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