Misc improvements to the ADAM exercise.

This patch improves clarity of some issues encountered during AmpCamp 5:

* Improve accuracy of reported size reduction from SAM to ADAM format
* Show users how to add $HADOOP_HOME/*.jar, $HADOOP_HOME/lib/*.jar to classpath
* Show users how to inspect parquet footer in a more legible format
* The ADAM Webapp must be opened from `usb/adam/`, not `usb/`

Fixes issues #171, #172, #173.