Query Builder uses wrapped query

Hi

Ive knocked this together this morning, its not finished and I havn't tested it manually.

- DocumentManager returns wrapped PHPCR QueryBuilder
- Query builder uses a wrapper ODM query
- Can call ->execute() on returned query object and get Documents

I think that the expression builder thing discussed in https://github.com/phpcr/phpcr-utils/pull/28 is a separate issue.

What do you think?