Add class "quantity" #1510

[nelekoehler]

Summary of the discussion

As described in #1510 and #1752 we want to restructure quantity values. Therefore we need a class "quantity", which I added in this pull request. The definition has been derived from the International vocabulary of metrology — Basic and general concepts and associated terms (VIM).
Based on this implementation some existing entities have to be reclassified in following PRs.

Add

• Added a new class "quantity": A quantity is a quality of a material entity where the quality has a quantifiably magnitude (i.e. quantity value) that can be expressed as a number and a unit.

Workflow checklist

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• 📝 Update the CHANGELOG.md
• 📙 Add #'s to term tracker item

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[stap-m]

Looks good. We might add the axiom quantity 'has quantity value' some 'quantity value'.

[l-emele]

Looks good. We might add the axiom quantity 'has quantity value' some 'quantity value'.

Are there quantities which cannot have quantity values? I don't think so. Thus I suggest to make it an equivalent class: quantity EquivalentTo: quality and 'has quantity value' some 'quantity value'.