With exercism/exercism.io@54e1df3, we can now gather exercises into a
subdirectory. By separating the language track files from the
configuration and management files, it is easier to read the project.

- move gradle config under "exercises" too as it would make a mess
  otherwise.

- enable compilation during CI build only for those that currently pass.
  (let's tackle the failing tests+example code one at a time).

Missed the example file. Woah --> Whoa

This is the complete skeleton for enabling Java, from curriculum
through the first exercise. Java is listed in the main curriculum.rb
but commented out; we will activate once there are a sufficient body
of exercises ported.

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.