Merge pull request #1855 from akeneo/PIM-3443-2

PIM-3443: Fix prices export and add spec
PIM-3446: limit the warning display to 100 in import/export
Merge branch 'PIM-3446' into PIM-3446-merge
Merge pull request #1858 from akeneo/PIM-3446-merge

PIM-3446 merge to master