Improved networkx mermaid graph visualisation

[Carwyn Pelley (cpelley)]

• Clicking on table rows centres the mermaid graph on the corresponding node.

• Better handling of layering (overcoming issue with some region not allowing graph to be dragged).
• Clicking on a node now adds a link to #diag-top-left-controls.
  • This makes it easier to open collapsed graphing especially when slicking on mermaid subgraphs as there isn't really good placement for anchor links.

• Support for unhashable types for holding onto sets of node data (required for EPP visualisation).
• Mermaid graph theme now correctly changes as we change the page theme.
  • Chosen theme also remembered when revisiting the page.