Fixes for instruments

[jmillanacosta]

• [ ] Commercial instruments should not be classes, but instances.

For instance: Malvern Zetasizer is defined as a subclass of instrument. It should be defined as an instance of dynamic light scattering instrument

• [ ] Many classes are defined as assays and instruments simulataneously (e.g. dynamic light scattering instrument)

• [ ] Predicates missing for instruments - detection methods