PIM-2492: Implements simple option filter on empty value
PIM-2492: Make option filter empty work
PIM-2492: Clean OptionFilter class
PIM-2492: Filter by multi/simple values
PIM-2492: Filter by empty value for simpleselect
PIM-2492: Clean phpdoc
PIM-2492: Allow to filter by empty multi value
PIM-2492: Update scenarios
PIM-2492: update scenario
PIM-2492: Update behavior of ORM base filter
PIM-2492: Update metric filtering scenario
PIM-2492: Change behavior for empty filtering on metric fields
PIM-2492: Change behavior on price filter
PIM-2492: Add phpdoc
PIM-2492: Update price scenario
PIM-2492: Change behavior of OptionFilter ORM
PIM-2492: Change behavior for Options filter
PIM-2492: Update empty filter for multi options
Merge branch 'master' into PIM-2492
Merge branch 'master' into PIM-2492