Display reason for node mutation on hover and highlight the reason by coloring the nodes

[EatingW]

Poker planning notes:

• Modify the GraphNode class to have an additional attribute for how it changed and why it changed.
• Whether to send the mutation list to the client instead? And the client would change node style based on mutation list
  • This means we can technically do everything in the client? TBD
• Timeline view don't need to display reason or highlight. This applies only to prev/next buttons.
• On the client side, adjust the styling of the node based on the mutation
• How to know what changed when navigating to previous?
  • We would have the mutation from N to N+1.
  • Can have a function to negate the mutation for coloring and displaying the reason
• What are some reasons for mutation?
  • Tools may append some reason to the mutation (any string)
  • Additional information for user to debug the graph. E.g. adding new synthetic node.
• How to consider this done:
  • Demo to show highlighting and reason for mutation on next/prev
  • Unit test for GraphNode's additional attribute.

Proposed estimate: 4