OPENDJ-1472 : File based changelog : optimize random seek in each log file
CR-3727

[Note: real merge of all changelog.file package content to be done in one shot in
 a future commit]

Implements read and write with blocks, to enable binary search.

* New BlockLogReader class: read records sequentially or using
 binary search provided a key
 
* New BlockLogWriter class: write records by blocks

* New BlockLogReaderWriterTest class : tests read/write with blocks

* Update LogFile : delegate responsibility for read/write to BlockLogXXX

* Add method ByteStringBuilder#append(DataInput, int) to avoid 
 byte array copy

* Minor changes in other files