Favor off-heap over on-heap LongArrays

to reduce unnecessary strain on GC, since these arrays often come in great
sizes.
Doesn't write page in batching page cache if there are no changes
Less garbage around encoding/decoding labels for nodes
Generic store processing steps in batch immporter
Ability to release memory at will in the batch importer

by making sure that only the ParallelBatchImporter holds references to the
high-volume cache objects and so can release them by setting to null.
Batch importer stages added for populating count store
CSV input integration test verifies counts after import
Also tracks ANY counts in ParallelBatchImporter
Exposes static method for reading high id from id file
Extended StoreFile#move into #fileOperation with either COPY or MOVE
StoreMigrator can tell batch importer things about the legacy store

High token ids which are essential for some calculations inside the batch importer
to know those high ids up front.
Also the last committed transaction id, so that the counts store is marked
with that id when writing it.
Fixes a label cache issue where high label id was 0

Also made LongArray#setAll more convenient to use by returning itself.
Merge pull request #3312 from tinwelint/2.2-bip-counts

Batch importer updates counts in counts store