Enable user to skip last Simulation step

The last step before the acutal import of data "Do an import simulation" triggers a simulation that is not always necessary.
Moreover, if the amount of data is big, it will end-up on a 504 error, after which resume to the import task is impossible.

Proposal: Add in the UI a "skip simulation" option, to enable advanced users to trigger import of data without this last verification.

Thanks!