Add support for multi person inventory

[gosanke]

Adding a field in inventory for designating an item to a person and adding filtering on the person when building packs.
I'm usually the one planning the packs for my family (wife and kids), and it would be great to be able to build several packs for the individuals in one place.
Stuff like clothes, backpacks, poles, other wearables, etc., is personal in size and weight, but then I distribute all the other stuff according to ability (size, age, fitness, etc.).
The feature of having everyone's gear in one inventory and being able to filter on a person when building would be killer.