PIM-3209: Fix import running even with wrong file

*Added verification of the file extention before the launch of the job
*Added new behats in order to verify that the file extention is allowed or not
PIM-3234 Uses category ids to filter products
PIM-3234 Fixes unclassified category filter
PIM-3234 Changelog on bugfix
PIM-3234 : extract method to ease override
PIM-3209: Fix import running even with wrong file

*Added verification of the file extention before the launch of the job
*Added new behats in order to verify that the file extention is allowed or not