Add Travis CI support

This pull request adds support for using Travis CI. It runs the test suite on OpenJDK 6, OpenJDK 7, and Oracle JDK 7 (these are the only supported JDK versions on Travis CI). This pull request also adds a build status badge to the README that is displayed when this repo is viewed on GitHub. It currently says Unknown, as the badge points to the Esri project so no changes will be needed (code wise) if this PR is merged. Someone from Esri with a commit bit on the repo will need to log into Travis CI (with their GitHub account) and turn on tracking for the repo.