several versions of labels and axes names

[gdementen]

mostly for output/reporting
short/long
language
...

[gdementen]

I am unsure what the relation between these translations and other metadata should be. Translations probably need to have a special status, so that they can be used in display func and viewer, but we might want to add the possibility to add arbitrary metadata to individual labels and axes and thus store "translations" along with that metadata.

related to #280, #733 (they should both use this new functionality) and to a lesser extent #689