Merge branch 'PIM-3266-stable' into PIM-3266

Conflicts:
	features/export/export_attributes.feature
	src/Pim/Bundle/BaseConnectorBundle/Processor/CategoryProcessor.php
PIM-2109 Separate the columns button from the refresh and reset grid buttons
PIM-2106 Change the grid column picker title
PIM-2576 : add an information message when there is no common attribute
Merge pull request #1681 from akeneo/PIM-2576

PIM-2576 : add an information message when there is no common attribute
Merge pull request #1682 from akeneo/PIM-2109

PIM-2109 Separate the columns button from the refresh and reset buttons
PIM-3092 Create a dedicated category index page
PIM-3092: New index page for attribute groups
Merge pull request #1679 from akeneo/PIM-3092

PIM-3092 Add index pages for attribute groups and categories
PIM-3266: set the ManagerRegistry as mandatory for the TransformerProcessor
PIM-3266: fix Behat scenarios broken during the merge from stable branch
Merge pull request #1673 from akeneo/PIM-3266

PIM-3266: do not flush skipped items during an import
PIM-3282: fix the grid filters that can be set as json in the request