Add item sorting in the bag

[milkyroute]

The goal is to add different ways to sort the items in the bag. Currently there is only one: alphabetical. Nothing is currently planned in the interface to implement this: several options are possible (dedicated keys; a key that opens a menu...). Examples of sorting methods could be "last used" or "quantity". There should also be an option to reverse the sorting order.

This issue is not urgent and will not be pushed forward until several versions. It is, however, needed before the first playable version of the game is released.