Make references allow single select

[kedelima]

The idea of this Issue is to have a property of the "references" type and allowing a singular choice (multiple: false|null).
To facilitate switching between singular and multiple selection afterwards.

Current Problem: Within a nodeType, when type is set to type: references and it is not multiple: true, when selecting a single entry, it doesn't apply the changes.

I will provide a snippet, if anything is unclear or needs more details, please let me know.

Thanks for the hard work and any further support is much appreciated.

 categories:
       type: references
       ui:
         label: News Category
         inspector:
           group: newssettings
           editor: 'Neos.Neos/Inspector/Editors/SelectBoxEditor'
           editorOptions:
             dataSourceIdentifier: 'tms-select-nodedata'
             dataSourceDisableCaching: true
             #multiple: true
             dataSourceAdditionalData:
               nodeTypes: ['Foo.Bar:Tag.Category']
               #startingPoint: /sites

[paavo]

Any thoughts about an Implementation @jobee?