Feat/item based encumbrance

[anthonyronda]

Adds Item-based encumbrance as an encumbrance option in the settings menu

Consider this a fairly early pass on the feature, due to the fact that a couple of things are really clunky about it

• it migrates your heavy armour to 2 item slots, and your two-handed weapons to 2 too
• it should correctly show you whether your packed or your equipped items are slowing you most (although this is probably confusing)
• all the item sheets will show you the input box for weight or for item based encumbrance depending on which type is enabled
• there were a lot of other considerations I had to make but I forget most of them