Proper game state structure

[ethanmoffat]

Currently, persisted data in EndlessClient is stored in a repository/provider pattern. It would be nice to store this is a JSON-serializable GameState structure behind the repositories/providers and have each repository/provider expose just a specific piece of the game state. The interfaces don't have to change; their implementation can just draw from a global GameState provider.

This would really only be an improvement for debugging purposes, and I might ultimately decide not to do it since it would be a huge change.