Reinstates a batching page cache for batch import

Basically it's the "page cache" version of
https://github.com/neo4j/neo4j/blob/2.1.2/community/kernel/src/main/java/org/neo4j/unsafe/impl/batchimport/store/BatchFriendlyWindowPoolFactory.java

such that there's only one page per store in memory all the time and it
moves along with the batch importer "cursor", no other store file memory required.
Merge pull request #2640 from tinwelint/2.2-batch-page-cache

Reinstates a batching page cache for batch import
Add tests for TransactionRepresentationStoreApplier

Remove duplicated call to updateIdGenerators since it is called by NeoTransactionStoreApplier
 when in recovery
Add tests for NeoTransactionIndexApplier

Add equals and hashcode methods to simplify testing
Slightly changed the interdace of LazyIndexUpdates to simplify testing
Add tests for NeoTransactionStoreApplier

Code cleanups