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

- adjusted "etl" as it has "starter" code.

- move example.java so we can refer to it in Gradle as a soureSet.
- Java requires public classes be contained in identically-named files.
- using latest Travis infrastructure (better, stronger, faster).
- each piece of travis config has been confirmed as minimum necessary at
  this time.
  - without JDK specified, would run with default (Java 7)
  - without TERM=dumb, travis output is unreadable.

We will be relying on people installing gradle themselves. The documentation
on help.exercism.io has been updated with instructions for both Windows and Mac.