Describe the bug
The ProcedureModel has a couple of bugs, based on recent experience:

1. A node dragged from the palette cannot be added on to the very end of a procedure.
2. Adding a node prior to the current last node, and then trying to move the last node up above the newly-added one (thus putting the new node at the end of the procedure) causes a segfault.
3. A node added to an IfValueInRange node branch cannot then be deleted (IfValueInRange node specific?)