Include state of Path outfit in save game

Fix for #162.

Using the StateManager:

* Save changes to state of the path outfit in 'path[resource]' whenever a resource is incremented/decremented.
* Clear out 'path' on embarking (just after the resources are decremented from the stores).
* Load the saved 'path' outfit when initialising the path screen, or use an empty object (as previously) if it doesn't exist.

It's my first change to ADR, so I expect I'm missing something!

Perhaps the State shouldn't be used for 'temporary' storage like this? It does seem like the simplest way to get the contents of the path 'outfit' to persist/load with the save game, though.