Introduce get_job tree per archetype

[lstrzebinczyk]

Any time a person chooses a new task, he goes through Settlement#get_job. However, we can simplify this rapidly by creating a smaller task job for each archetype: leader, gatherer and so on.

It seams reasonable, that if person thinks about what to do, he first goes through things he personally things he needs to do, just then he might think about what the settlement needs. The settlement could then further pass such job asks to buildings.

This is a discussion issue, please share your thoughts.