* Register added nodes into EditorOnly expression collection to be saved/displayed correctly
* Fix conversion invalidation when a node is deleted
* Change Substrate version meaning:
* -1 no conversion has run
* 0 the conversion fonction has run and no conversion was done. Or the material has been changed/touched since its conversion
* >=0 the conversion function has run
#rb sebastien.hillaire
[CL 36760583 by charles derousiers in 5.5 branch]