kiji-schema: SCHEMA-806. Revamp (fix and improve) kiji shell script.

 - Improve DEBUG mode (logs file:line)
 - Document environment variables.
 - Emit warnings when required environment variables are not set.
 - Add kiji env-check to dump and validate the environment.
 - Document priorities between environment and path.
 - Disable Maven assembly filtering of shell-scripts.
 - Beef-up profiling enable/disable scripts.

issue: https://jira.kiji.org/browse/SCHEMA-806
review: https://review.kiji.org/r/1903
commit: https://github.com/kijiproject/kiji-schema/commit/3818c4e3cd7f01985fadf3f66819761da328a124