Updated bundle to use Composer and other minor changes

* Added composer.json file
* Tweaked the phpunit.xml file
* Migrated test suite to use composer's autoloader instead of old vendor install. 
  * Run composer install in package root, then just run phpunit in package root. 
  * All tests still 100% pass and 100% coverage
* Removed various parts of .gitignore (OS and editor definitions), which should instead be in a global gitignore, not in a package-specific file
* Updated travis.yml file (May need to be tweaked, as I cannot test it from my local form AFAIK)