Added context menus to inventory

Also added a language handler which will be used later on for reading
text strings (i.e. "Necklace of Feeding") from a file, allowing custom
languages as well as stock ones.
Modified the base gui manager to render in reverse order, so the
top-most elements are now what would get click priority. Also means
newly added elements via elems.add will appear on top.
Dying now closes any menu that doesn't pause the game (inventory, for
instance).