Create archive file from ReferenceEditQuantity choosing among the children classes of the defined type

In the following schema, the sub_section steps_referenced contains a ReferenceEditQuantity where we are supposed to specify a type and then to fish some archive file in NOMAD or to create a new one.

definitions:
  name: 'MOVPE Experiment (IKZ Ga2O3)'
  sections:
    My_activity:
      base_sections:
      - nomad.datamodel.metainfo.eln.Activity
      - nomad.datamodel.data.EntryData
      quantity:
        method:
          type: str
          default: "My Custom Activity"
    SubstratePreProcess:
      m_annotations:
        eln:
      quantities:
        method:
          type: str
          default: "MOVPE IKZ Substrate Pre-Process"
      sub_sections:
        steps_same_entry:
          repeats: true
          section: nomad.datamodel.metainfo.eln.Activity
        steps_referenced:
          repeats: true
          section:
            quantities:
              step:
                type: nomad.datamodel.metainfo.eln.Activity
                m_annotations:
                  eln:
                    component: ReferenceEditQuantity

A problem arises when the type I specify is not an EntryData as the "plus button" is not there.

It happens that we want to create archives of some subclass of the specified type from the plus button (for example a subclass of Activity), like it used to happen for the sub_sections living in the same entry (look at the steps_same_entry class in the schema attached, it gives rise to a drop down menu).

Another point to notice is that the dropdown menu the custom schema classes are also shown (My_activity) together to the ones in NOMAD! Would be beneficial to show both sets also for the ReferenceEditQuantity.

I described this issue to @mnakh

@hnaesstroem I tag you to inform you about this. I guess it might be useful for you too, whenever the user wants to build a sequence of Activities manually from the ELN