Make `Identifier` public (cherry picked from commit 604a9b07f3508fd8c4a5df25e7d425c442ee84df)
Make `Identifier` public
(cherry picked from commit 604a9b07f3508fd8c4a5df25e7d425c442ee84df)

Conflicts:
	server/src/main/java/org/spine3/server/projection/BeamCatchUp.java -
	removed for now

SpineEventEngine/core-java,SpineEventEngine/core-java,SpineEventEngine/core-java