With large imports it has a large impact on performances and isn't really useful.
Instead, write an IMPORT event, which let client using the history service resync its DB.
-> 15k link import done in 6 seconds.
Fixes#985
Use case: rest API service
* saved by default in data/history
* same format as datastore.php
* traced events:
* save/edit/delete link
* change settings or plugins settings
* rename tag
