Fix #112 - Add continuous integration via Travis CI.

Increment build tools to 19.0.1, apparently 19.0.0 aren't available via Travis CI (fetching fails with HTTP 404 error).

Matching buildToolsVersion in build.gradle with build tools version in .travis.yml file.

Squashed all old commits and rebased on OneBusAway:master, so hopefully it builds on Travis this time.