Consistent event deduplication between loader and repeater

[istreeter]

As described in #144, the repeater uses event_id as an insert id, which means two events with the same id are deduplicated when inserted to the table. The loader does no such event deduplication.

Event deduplication should at least be consistent. Either, a user should expect two events with the same event_id to be both in the table, or not. It should not depend on which component loaded the event.

If we go the route of full deduplication then we should understand the performance impact first. We could consider making this a configurable option, to toggle either behaviour.