PIM-3434: throw exception when media file does not exist
Merge pull request #1830 from akeneo/PIM-3434

PIM-3434: throw exception when media file does not exist
PIM-3326-stable-static-analysis: Fix checkstyle
Merge pull request #1841 from akeneo/PIM-3326-stable-static-analysis

PIM-3326-stable-static-analysis: Fix checkstyle
PIM-3436: wysiwyg fix
Merge pull request #1835 from akeneo/PIM-3436

PIM-3436: wysiwyg fix (load them asynchronously)
PIM-3369 : stops the product import with a detailed notice when
encounters issues with field formatting

Conflicts:
	CHANGELOG.md
PIM-3369 : fix issue with optional currency in a csv field
PIM-3369 : fix the optional two fields case for metric import
PIM-3369 : add scenario on invalid headers