Restrict use of '/' in node-names to managed nodes only - name clashes

[RubendeBruin]

Prefixes in node-names are used to avoid name clashes between managed nodes.
This can fail if a normal node exists using the same pattern. This can easily happen if a managed structure is dissolved.

Proposal:

• reserve '/' in node-names for managed nodes only
• when a node becomes un-managed, change the name accordingly by replacing / by _ : Sling1/SpliceA --> Sling1_SpliceA
• enforce this in the node editor