Batch writer thread empties buffer into channel

instead of each append call, which allows for less calls to
FileChannel#write and less I/O wait for append threads.
Synchronized shutdown, since the log channel needs external synchronization
Remove unused utility code
Removes auto-boxing from CSV primitive-type extractors

By having each Extractor by state-ful and have specific accessor methods.
Merge pull request #3310 from chrisvest/2.2-remove-unused

[2.2] Remove unused utility code
Merge pull request #3283 from tinwelint/2.2-empty-log-buffer-in-force-thread

[2.2] Batch writer thread empties buffer into channel
Merge pull request #3311 from tinwelint/2.2-no-csv-boxing

[2.2] Removes auto-boxing from CSV primitive-type extractors
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
Garbage-free alternative to putting encoding labels for a node
Generic store processing steps in batch immporter
Ability to release memory at will in the batch importer
Batch importer stages added for populating count store
CSV input integration test verifies counts after import