Add a item_id column that will store the id of the data_type for which the event occurred.
Propose event types directly from DropDown menu (options). We don't need the event_types table.
Offer an upgrade procedure to re-import the data stored in pipet_events into the events table with links to pipets. Indeed, after upgrading from v1 to v2.0.1, what was in pipet_histories is now in table pipet_events. We must store this as events and then drop the pipet_events table.