Add method to split node and create subjunctive node at runtime

[jeffreyguenther]

Take an existing instance of a node and split into two alternatives.

The basic algorithm:

• Create a subjunctive node
• Name the subjunctive node
• Add original instance to subjunctive node
• Refactor all reference to original instance to subjunctive node's active node. Keep the port the same.
• Remove production of original instance from graph definition
• Add production of subjunctive node to graph instance
• Create instance of split node with the right arguments
• Update all existing system states to include new active subjunct map entry
• Create new system state for the new subjunctive node. Keep all of the same subjuncts from the state where the split originated. Add an entry for the new subjunctive node with the newly created instance as the active subjunct.