Copy constructor for IndexerConfBuilder

Allow creating a new IndexerConfBuilder instance based on from
an existing IndexerConf instance.
Initial rough cut of MapReduce indexing tool

Based on a forked version of the standard MapReduceIndexerTool
to set up the basic structure of reuse between the
HBaseMapReduceIndexerTool and the standard MapReduceIndexerTool.

The ForkedMapReduceIndexerTool added in this commit is intended
to be removed as soon as the standard MapReduceIndexerTool has
been updated for easier reuse.