Misc improvements to the ADAM exercise.

[kimballa]

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 $HADOOPHOME/.jar, $HADOOPHOME/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.

[jey]

@fnothaft: could you review this? thanks!

[fnothaft]

+1, these are great changes. Thanks @kimballa!