Replace "outfit" and "right_hand_wield" with many "attach_*" properties

It's tricky to update the outfit property when only changing one value. Better to instead use multiple separate properties.
To make it more general we should replace both the "outfit" and the "right_hand_wield" property with multiple "attach_*" properties.
For example "attach_hand_primary", "attach_head". This can also be used for attaching things that aren't worn, like attaching a painting to a wall.

Available attach points are defined in the Type, with null values by default. Things can only be attached to existing attach points.