Simplified loops in import/rebuild-index code.


Importer.java:
Set the indexKey on the IndexOutputBuffer inside indexBufferMap field + added an IndexKey parameter to getNewIndexBuffer() + simplified code in flushIndexBuffers() as a ceonsequence
In IndexBBWriteTask:
- In call() always create the key buffer, removed duplicated code in a loop.
- Moved call to keyCount.incrementAndGet() from call() to addToDB().
In ScratchFileWriterTask class:
- In call(), removed duplicated code in a loop
- Removed insertOrDeleteKey(), superseded by the more complete insertOrDeleteKeyCheckEntryLimit()
- Renamed insertOrDeleteKeyCheckEntryLimit() to appendNextEntryIDToStream()
- In writeIndexBuffer() and writeIndexBuffers(), simplified the code
In IndexManager class, renamed field limit to indexEntryLimit + changed getter.

IndexInputBuffer.java:
Changed compare(ByteStringBuilder, Integer) to isSameKeyAndIndexID(ByteStringBuilder, Integer) + made it null safe

IndexOutputBuffer.java:
Changed recordsEqual(byte[], int) to isSameKeyAndIndexID(byte[], int) + made it null safe
Renamed byteArraysEqual() to sameKeyAndIndexID().