XD-987: HDFS to mongo export job

Create
  - spring-xd-extension-mongodb
  - hdfsmongodb module

Move existing mongo code from hadoop extension to new mongodb one.
Add new TupleItemWriter which allows a specific identity field to be
chosen if required instead of the generated Tuple UUID.
XD-988: Batch export from HDFS to JDBC.

Note the issue with Spring HADOOP (SHDP-201) which prevents the easy use
of both HDFS and file resources in the same module, thus preventing the
use of the same DB initialization code from the file->JBDC module. This
is commented out for now and relies on manually pre-creating the
database table.
cleaning up redis keys for composed module