[BUG] Ref sub-elements drop the `Ref` part in their name

[remytorro]

Describe the bug
References drop the Ref in the MMApp JSON compared to the XSD definition, making it difficult to recognize the attribute. In the following example, the XSD-compatible sub-elements (not even attributes!) would be ExitationFilterRef, StandardDichroicRef and EmissionFilterRef:

        {
            "Name": "DAPI A4 ET k",
            "ID": "8ffc8eb1-fd54-49d0-90a0-76d336b7bba3",
            "Tier": 1,
            "Schema_ID": "FilterCube.json",
            "PositionX": 639.9899499999999,
            "PositionY": 758.6305000000001,
            "PositionZ": 0,
            "Width": 70.4543,
            "Height": 69.9062,
            "OffsetX": 0,
            "OffsetY": 0,
            "OccupiedSpot": "FluorescenceLightPath.FilterCube_0",
            "Manufacturer": "Leica Microsystems",
            "Model": "DAPI A4 k",
            "CatalogNumber": "11504203",
            "ExcitationFilter": "ExcitationFilter/cc9eea58-bb85-40e4-84dd-2844fb2c0416",
            "StandardDichroic": "StandardDichroic/729aa4d6-6616-46ed-b60e-8449f4a3f2ee",
            "EmissionFilter": "EmissionFilter/52679ad7-eac0-4d94-91b0-37c008bd7a42",
            "NrOfSlots": 3,
            "ModelVersion": "2.01.1",
            "Extension": "Core",
            "Domain": "MicroscopeHardwareSpecifications",
            "Category": "FluorescenceLightPath"
        },

Adding the Ref in the config would help us to find the proper sub-element. Event more convenient would be to follow the pattern of sub-elements by writing:

        {
            ...
            "ExcitationFilterRef": [{"ID": "Filter:cc9eea58-bb85-40e4-84dd-2844fb2c0416"}],
            "StandardDichroicRef": [{"ID": "Filter:729aa4d6-6616-46ed-b60e-8449f4a3f2ee"}],
            "EmissionFilterRef": [{"ID": "Filter:52679ad7-eac0-4d94-91b0-37c008bd7a42"}],
            ...
        },

The XSD-compatible XML for this would be something like:

    <FilterCube Manufacturer="MeMe" Model="Cool" CatalogNumber="1324"
        ID="FilterCube:8166cf37-e404-4325-bbea-f8aef8ece42a" Name="Cube1" Motorized="0"
        OpticsHolderPosition="1">
        <ExcitationFilterRef ID="ExcitationFilter:cf644607-813e-4206-830d-1fa1d97d29cb"></ExcitationFilterRef>
        <EmissionFilterRef ID="EmissionFilter:5ff8bf50-64b5-4306-9e9f-894dfd952c2f"></EmissionFilterRef>
    </FilterCube>