PIM-1430 : declare guesser as services
PIM-1430 : add a chained guesser that is able to contains and runs many
guessers
PIM-1430 : add a compiler pass to register every guessers in chained
guesser
PIM-1430 : inject chained update guesser in version builder to detect
any entities that need to be versioned
PIM-1430 : update changelog
PIM-1430 : clean up services definitions
PIM-1430 : fix unit tests
Merge branch 'master' into refactor/chained_guesser

Conflicts:
	CHANGELOG.md
Merge pull request #437 from akeneo/refactor/chained_guesser

Refactor/chained guesser