Composed units need relations

[chrwm]

Description of the issue

When units are composed the concept per e.g. €/MW and times e.g. m/s^2 are needed

Ideas of solution

Add per Add times

Workflow checklist

• [x] 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

[l-emele]

Solution from physical OEO dev meeting:

m/s EquivalentTo: unit and has_linear_unit_numerator m and has_denominator s
kg/m³ has_numerator kg and has_cubed_denominator m

km/s has_numerator km and has_denominator s

MWh/km has numerator (has_prefix mega and Wh) and 

Wh has_numerator W and has_numerator h

relation_between_units as subclasses of has_part
has_unit_numerator: A relation between a (composed) unit A and a unit B in which B is in the numerator of unit A.
    has_linear_unit_numerator: A relation between a (composed) unit A and a unit B in which B is in the numerator of unit A with exponent 1.
    has_squared_unit_numerator
    has_cubed_unit_numerator
has_unit_denominator
    has_linear_unit_denominator
    has_squared_unit_denominator
    has_cubed_unit_denominator

I will implement.