Conflicts:
	src/jio.storage/replicatestorage.js
	test/jio.storage/replicatestorage.tests.js

Attachments are synchronized only of explicitely activated from the jIO configuration.
Replication deletes a document only if it doesn't contain any attachment.

Thanks to Cedric Leninivin for his work on this topic.

/reviewed-on nexedi/jio!42

It allow to check recursively if a storage support bulk.

`jIO.util.stringify` was raising if the value of an object was undefined, this changes fix it and provides the same behaviour as the standard `JSON.stringify`

/reviewed-on nexedi/jio!41

@seb, please review

/reviewed-on !37