BENTO-11. Add 'bento upgrade' command.

Checks for a new version, then upgrades to it if available.
Test plan is at jira.kiji.org/browse/BENTO-11.

Also adds codename and release manifest.

* add <codename>albacore</codename> pom property
* rename output to kiji-bento-${codename}/
* add bento-version.txt file advertising what version we run.

r: kiyan
https://review.kiji.org/r/139/