Set Custom Field Contexts Default Values

Sets default for contexts of a custom field. Default are defined using these objects: * `CustomFieldContextDefaultValueDate` (type `datepicker`) for date fields. * `CustomFieldContextDefaultValueDateTime` (type `datetimepicker`) for date-time fields. * `CustomFieldContextDefaultValueSingleOption` (type `option.single`) for single choice select lists and radio buttons. * `CustomFieldContextDefaultValueMultipleOption` (type `option.multiple`) for multiple choice select l...