Added acquiring and droppping of items

-PLayer can 'take' items from the world, these are added into the inventory
-Player can 'drop' items into the world. The item will remain in the area where it was dropped
Added in inventory pre-requisite checks for conversation topics

-PLayer must have a certain item in their inventory before they can access certain conversation branches
Refactored direction commands

-Put all commands under subobject called Direction, rather than individual objects for each direction