Associate equipment, etc., with individual workers

[kingjon3377]

While some equipment is shared by all workers in a unit, some ought to be specific to an individual worker. And animals ought to be treated similarly. We need this to be able to start on a combat simulator, and also for #31; once animals (mounts) are associated with workers, we can start deducing unit MP instead of always requiring the user to enter it.

On the other hand, sometimes multiple workers need to be associated with a singular piece of equipment, or perhaps even (in the case of something like an elephant) an individual animal.

[kingjon3377]

Once equipment can be associated with individual workers, we should add a check to the map-checker app to warn about equipment like uniforms being placed in a fortress.

[kingjon3377]

We'll also want to add the ability to move equipment onto and off of workers to the worker management app.