Allow setting primary language on vocabulary level

[ledsoft]

Description

Currently, primary language (language in which all terms must have a label) is set per TermIt instance. This requirement is too coarse for instances where international cooperation may occur. I, as a user, want to be able to set the primary language on vocabulary level.

Usage

When a single TermIt instance is used to manage vocabularies in multiple languages.

Usefulness

1. Cannot do it without this feature

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