Migrate old file-based game-data to use the graph library

[oubiwann]

Part of:

• 41

Depends on:

• 68

Tasks:

• [x] #45
• [ ] Support serialising graph data
  • [ ] now that vertex label data has id in it, all that's needed for the vertex is just the label data
  • [ ] for the edge we need "from", "to", and edge label data
  • [ ] pretty sure that's all that is needed ...
• [ ] Support de-serialising graph data (to Erlang digraph)
• [ ] Serialise old game data and write to new files
• [ ] Ensure that when game loads, these new files are read