Bugfix: try-with-resources closes 'is', but 'is' is stored internally in BufferInputStream to read from

See merge request !2

- added workaround to log errors if IOException thrown in retrieveEntity()

- added new plugin param "BUFF_SIZE" to not infer with "BLOCK_SIZE" of 8192 requested by ExL SC07081803

  a) old value is null or
  b) newvalue is equivalent to old value
  otherwise it results in logic error if a copy from operational to
  permanent fails first and will be triggered again

- use java.nio.file.Files.newInputStream instead of FileInputStream
- use java.nio.file.Files.newOutputStream instead of FileOutputStream
- minor simplifications

- refactoring, use faster java.nio.channels.FileChannel.transferFrom() if both streams are file streams

- fixed getBlockSize() to parse BLOCK_SIZE once only

- fixed checkFixityAbs(), disabled parallel checks, because Rosetta is not threadsafe

- fixed bug, checkFixity() expects a storedEntityIdentifier