Job trees

There are a few things in the project that could become a good foundation for a Job tree. For example, you can see the way that `JobGrowthStats.csv` is tied to a `Job`. You could create another `csv` that would hold things like a column with the name of a Job, a column with an experience threshold, and a column with a new Job type that is available as a result. In that way you could structure all possible Job promotions. When changing Jobs you can use the `Employ` and `UnEmploy` methods. You just need the game fleshed out well enough to provide the UI to let a player choose when to change jobs and what to change into.