Add disposition / quality of `quantity value`: nominal versus real

[l-emele]

Description of the issue

In issue #1487 we want to add the following classes:

• constant monetary value / price
• nominal monetary value / price
• gross domestic product real growth rate
• gross domestic product nominal growth rate
• nominal GDP
• real GDP

To solve this, we probably needs some kind of multi-hierarchy

• ~economic value (already implemented)~ deprecated
• quantity value
  • has disposition / quality constant or nominal

Ideas of solution

If you already have ideas for the solution describe them here

Workflow checklist

• [ ] I discussed the issue with someone else than me before working on a solution
• [ ] I already read the latest version of the workflow for this repository
• [ ] The goal of this ontology is clear to me

I am aware that

• [ ] every entry in the ontology should have a definition
• [ ] classes should arise from concepts rather than from words