Add tooling for rearranging the graph

[JackAtOmenApps]

• Inserting nodes on an edge (splitting an edge into two with a node in-between). Consider whether the existing edge properties should be mirrored to the two replacement edges, or if new values should be used. (aka: subdivision)
• Removing nodes - we can currently remove children nodes one-by-one, but I want to be able to specify a particular node and remove it, potentially with various strategies for how to handle its associated edges
  • 1. simply delete, potentially leaving a gap
  • 2. weld if there is only one parent and one child edge (aka: smoothing)
  • 3. delete, and cascade-delete downward
  • 4. Others?
• Moving the start/end of an edge to another node, with circular check
• Copy a section of the graph

[peter-stuart-turner]

Also keen to be able to move nodes around and change relationships