Search lucene refactoring

This is https://github.com/owncloud/apps/pull/1624 moved to this Repo. It does not change the database.xml but changes the way backgroundjobs are used to index new files and update changed files.

Also starts adding unit tests and initial README.md Will enable travis testing and add more tests in future PR.

@DeepDiver1975 @karlitschek @kabum see commit messages for detailed changes.
When working with the file objects it's best to pass the file object around instead of the path, this saves having to re-load the meta data from the cache.