Adding plural strings for units

[olinux]

For display purposes, it would be nice to register the plural for a unit in the controlled term (e.g. "years" for "year").

https://github.com/HumanBrainProject/openMINDS_controlledTerms/blob/d8bc03dce7c5764f80e2ced630dde4e572ffbb7b/schemas/unitOfMeasurement.schema.tpl.json#L1

[UlrikeS91]

I just closed the PR, thinking that this is not required anymore: #61.

In one of the comments, @lzehl was against adding plurals. But maybe worth discussing again?

[UlrikeS91]

PS: I'm keeping this issue in the controlledTerms-repo for now. This may affect the instances-repo as well, since all UnitOfMeasurement instances would need to be updated. But we can still move it when we see the need for it.

[lzehl]

@olinux @UlrikeS91 @apdavison I suggest we discuss this in our Dev meeting.

I would like to discuss the schema and registration of units in general, because I think they should be a bit more complex than our usual controlled term. I personally do not like that we are currently registering every multiples of a unit (g, kg, mg, ng, etc) and I'm missing explicit information (e.g. unit of what? (mass, time, etc), abbreviation, plurals for fullNames). I also would like to be able to more clearly register SI based units separate from other units.