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.
As noted above, imo it would be better to have seperate job for indexing one file (using write hooks) and one for indexing all unindexed files (maybe a timed job every ~30min or so)