KIJIMR-19. Adds MapReduceJobBuilder.withConf(Configuration)

Unambiguously sets the job base configuration.
Side-effect: job history recording now happens in both input/output Kiji instances.
KijiConfiguration is no longer used to locate the Kiji where to record.
Fixes a bug in mapper classes: contexts were not closed during cleanup().
Updates all tests to set base job configuration explicitly (now required).