Add custom Node type when importing trees

######Summary

Until now, every custome node types where deleted when you exit the page and you if you try to import a tree with custome node, you get an error.

With this version, importing a tree will create any custome node that doesn't exist yet. It will try to guess the node type from the json.

######About the code

When importing a tree, we go through all nodes and check if the node names is allready registered, if not, we create it. Then we use the normal .importFromJSON methode.