Implementing write chapter

we could do a method to convert all properties of a node to string representation (an array of name=>value(s) I guess) starting from [propsToXml](https://github.com/jackalope/jackalope-doctrine-dbal/blob/master/src/Jackalope/Transport/DoctrineDBAL/Client.php#L917) and put that into the base transport, then refactor doctrine-dbal to use that. 
you currently don't handle binaries which will pose a problem with longer binary data.