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.
I need the status changes to be reliable so I can skip files that somehow can't be indexed (then en error is stored in the db for that file and it is skipped, the next time the indexer job runs).