Node type editing, with FormField and FormList

This allows adding and removing custom fields from node types.
Currently does not work if the Node Type does not have any initial
custom field.

attract/application/modules/nodes/models.py

@@ -37,6 +37,9 @@ class NodeType(db.Model):
     description = db.Column(db.Text)
     url = db.Column(db.String(120), nullable=False)
 
+    custom_fields = db.relationship('CustomFields', backref='NodeType',
+        cascade="all, delete, delete-orphan")
+
     def __str__(self):
         return self.name
 
@@ -74,7 +77,6 @@ class Node(db.Model):
 class CustomFields(db.Model):
     id = db.Column(db.Integer, primary_key = True)
     node_type_id = db.Column(db.Integer(), db.ForeignKey(NodeType.id))
-    node_type = db.relationship(NodeType, backref='CustomField')
 
     field_type = db.Column(db.String(128))
     order = db.Column(db.Integer())