implement querybuilder hydrate array option

the query builder can currently hydrate to documents and to phpcr nodes. it should also be possible to hydrate the result into a plain array to avoid creating documents and get the direct query result. (btw note that '*' in sql2 does not mean all properties of a document, but just the path and some other basic things - you always need to specify all fields you want to retrieve explicitly in this case)

for the query builder base work and discussion see https://github.com/doctrine/phpcr-odm/pull/204