PIM-2438 : use string filter from filter bundle for media and file
attribute types
PIM-2438 : remove the attribute validation which forbids to use file and
media attribute type as filters
PIM-2438 : add a first implem of media filter based on string filter
PIM-2438 : implements the media filter for ORM ("like" case)
PIM-2438 : add implementation of empty for media filter
PIM-2438 Add a spec and behat scenario for media filter
PIM-2438 Add a media filter for Mongo
PIM-2438 Update changelog
PIM-2438 Set value to empty string when filtering by empty operator
Merge pull request #1805 from akeneo/PIM-2438

PIM-2438 : media and file filters for the grid