Bulk import - Mandatory fields are not taken into account

[arantzaetxebarria]

When importing an item from a template, it is not validated that the mandatory fields are filled in.
The result is that an item may be created without the required mandatory fields.

[arantzaetxebarria]

A validation has been introduced, so that if mandatory field(s) are not filled in, an error message is displayed to the user, detailing the field and the line where the error has occurred.