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
Merge pull request #1695 from akeneo/PIM-3209

PIM-3209: Import is running when we use upload and import with a file with wrong extension
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
Merge pull request #1697 from akeneo/PIM-3234

PIM-3234 Fixes category performance filter problem
Merge branch 'master' into PIM-3234-master
Merge pull request #1702 from akeneo/PIM-3234-master

PIM-3234 & PIM-3209 merge fix on master
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