java: Start track with Bob

The java.png icon is taken from http://findicons.com/icon/88943/java?id=89126,
released under a freeware license.

Describe how to minimally set-up Java and JUnit. (Future work may
try to see if we can get Locale.additional_files working and provide
build integration via Gradle or Maven.)

The BobTest is a straight up port of the Python Bob.

This starts the path of fixing #933.


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I did not do anything for testing other than `RACK_ENV=test rake test` however. Should I do something with the GUI or the command-line client? Probably. Getting this out for review and suggestions.