add CAPEX to the OEO

[madbkr]

Description of the issue

As mentioned in #1968 CAPEX is a term used in a definition in the new tasks module. Since this not a trivial concept I would like it to be added to the OEO.

Ideas of solution

I crafted a first idea for a definition:
Capital expenditures (CAPEX) are costs for physical assets (eg. and, equipment) including things like acquisition and maintenance. The asset has to have a useful life of more than on year.
It is calculated as (prior period Property, Plant and Equipment) - (current period Property, Plant and Equipment) + (current Depreciation)
CAPEX would be an alternative label.

Workflow checklist

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

I am aware that

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