As a user, I want to be able to understand why my import is not working

[RomuDeuxfois]

Description

Lack of granularity in error management at the import level (scenario/simulation)
When I import a simulation/scenario and something goes wrong, I have no information on what went wrong.
The import crashes globally.

Wouldn't it be better to do the import and display somewhere what went wrong?
Or have an import validation ?
(use what is already done for csv mapper maybe ?)

[EllynBsc]

2 issues raised with this problem:

Import of simulations/json : what error do we want to show ?
Import of xls: what error do we want to show ?