item: fix a conflict in field libraries

erp5_trade contains Base_viewTradeFieldLibrary which contain
my_dialog_mode_portal_type, which is a multi list field where user can
select multiple lines portal types. It is used in
DeliveryModule_viewDeliveryLineReportDialog/your_portal_type

erp5_item also contains Base_viewTradeFieldLibrary , for cases where
erp5_item extend trade module to select items. It also contains a
my_dialog_mode_portal_type field, where user can select item portal type.
That field is not a multi-list field, but a list-field. It is used in
DeliveryLine_viewSelectItemListDialog

So when erp5_item is installed, it overrides
Base_viewTradeFieldLibrary/my_dialog_mode_portal_type with a list field
instead of a multi-list field and breaks
DeliveryModule_viewDeliveryLineReportDialog, because user can no longer
select more than one portal type.

This renames the field in erp5_item, now we have:
 * Base_viewTradeFieldLibrary/my_dialog_mode_portal_type for movement
portal types
 * Base_viewTradeFieldLibrary/my_dialog_mode_item_portal_type for item
portal type