Defaul global unit system

We should be able to select very specific units like nanometer in custom global units (right now we can only select from a limited list e.g. meter etc but not nanometer). In a schema we should be able to set default global unit system including the custom units. For example, I have wavelenght in nanometer in my schema or temperature in °C, it should be customizable. At the moment the default display unit depends in the ELN annotations and can not be set in the level of non-eln quantities. The default global unit system should be in the level of section annotation.