Verifies if specified id is unique within the set.
    checkUniqueId(id, items, itemsDescription, objName)
    
    
        | id | string, id to verify | 
    
        | items | array, array of objects to check | 
    
        | itemsDescription | string, description of the item | 
    
        | objName | string, object name | 
    
 
Returns bool.
Description
This method is used internally to check if the id of a sidebar node, a toolbar item, or a tab is unique.