Edited Issue: Try to use IList, IDictionary or ReadOnlyCollection for returning types [774]

ODataModelBuilder.EntitySets property should be ReadOnlyCollection. same as Procedures and StructuralTypes properties;

Review StructuralTypeConfiguration/StructuralTypeConfiguration<T> as well;

ODataMediaTypeFormatters.Create() should return a IList<ODataMediaTypeFormatters>