reduce queries for fetching many node`s data

As described in the cmf-mailing list (https://groups.google.com/forum/#!topic/symfony-cmf-devs/Bv3REKYwT80), this would be my first changes for reducing queries. There is still an test issue i will solve later.
What about some `LIMIT, OFFSET` options for 
`DocumentManager::findMany()` (when calling this client from phpcr-odm), 
which defaults to `LIMIT = 999, OFFSET=0` in here?