Delete hard references

continuing the work of #24 - i plan to work on this january 13th


* check if the session is transaction capable and if it is and its not inside a transaction, start one
* first remove all properties of root node (in case they are hard references)
* delete hard references recursively on each but the first non-system child node - can we use a query for that?
* delete the non-system child nodes
* if we started a transaction, close it