SCHEMA-803. Harden KijiSchema shell script.

 - Delete extraneous? conf/ directory
 - Improve developer kiji script.
 - Remove unused/unusable foreground option
 - Normalize conditionals:
   * use [[ ... ]] instead of [ ... ]
   * use && instead of -a and || instead of -o
 - Fixes indentation some.
 - Normalize variables from $x to ${x}
 - More documentation and fixes.
 - Explicitate that shell ${kiji_schema_version} is Maven ${project.version}
 - Document ${KIJI_HOME}/lib/distribution origin.

issue: https://jira.kiji.org/browse/SCHEMA-803
review: https://review.kiji.org/r/1899