Implementing Search

This PR aims to implement the querying chapter of the PHPCR spec.

The general idea is that ZendLucene will be included by default but it could be replaced with other implementations (e.g. ElasticSearch).

I think it should ultimately be possible to support everything with Zend, although it would be easier (and I would imagine more performant) with ElasticSearch.

Some challenges:

- [x] Exact matching: Solved using a custom analyzer
- [x] Support for operators: Zend lucene doesn't support things like `> >= < <=` etc. It only supports ranges.
- [ ] Supports for all operands: Lowercase etc.
- [ ] Joins