Inventory - First Pass

First-pass of inventory implementation. Inventory shows items, stores
info in registry about item locations, and allows drag/drop of items.
Double-click for equipping items is sort of there but a little buggy.
Item drag/drop fix

Small fixes to the way drag/drop location is saved once a drag/drop
operation has finished. At this time, the continuous inventory
reordering is NOT yet supported (dragging onto another item, switch
which item is dragging).
Item Organization

Drag/drop is a lot more stable and less error prone. Draw order for
items is based on their column index, so labels should show up on top of
other items.
Equip enhancements

Equipping an item properly updates the inventoryitem label (if more
items remain) or removes the item from the inventory (if it was the only
one)
Item drop/junk

Item drop and junk are working properly, a large portion of the
inventory is now complete.