Revert "Revert "More parallellization in the batch importer""

This reverts commit 45b41deb576ca39663cac9dee8cc391421ab764d.

Conflicts:
	community/kernel/src/main/java/org/neo4j/kernel/impl/nioneo/xa/NeoStoreTransaction.java
	community/kernel/src/main/java/org/neo4j/unsafe/impl/batchimport/ParallellBatchImporter.java
	community/kernel/src/main/java/org/neo4j/unsafe/impl/batchimport/store/BatchingNeoStore.java
	community/kernel/src/main/java/org/neo4j/unsafe/impl/batchimport/store/BatchingWindowPoolFactory.java
	community/kernel/src/test/java/org/neo4j/unsafe/impl/batchimport/store/BatchFriendlyWindowPoolFactoryTest.java
Ring changed to SimplePool, which does not rely on acquire/release ordering