Clean up semantically close classes

[cmllezr]

• 'Chemische Eigenschaften Analyseverfahren' vs 'Analyseverfahren für die chemische Zusammensetzung'?? and other techniques
• Röntgenanalysator vs Röntgenbeugungsgerät ?? and other X-Ray techniques
• Nature constant could be deleted

The motivation behind these discussions:
By the defintions of the above mentioned classes it is unclear which class one should use.
Assays can / should have subclass axioms such as "assay measures characteristic X ". Thus, the clear separation between assays is desired