kiji-express: EXP-343. Add progress reporting to KijiExpress flows.

issue: https://jira.kiji.org/browse/EXP-343
review: https://review.kiji.org/r/1481
commit: https://github.com/kijiproject/kiji-express/commit/253cfbe91fb2d1db97908f0b8ad769eb6b283663