Add drag and drop functionality to items

[rorik]

Allow items to be drag and dropped into the outfit/accessories slots (as well as rearranging existing equipped items). Checks that the slot of the target (drop) is the same as source (drag), also avoids duplicated items from being equipped.

Not sure what to do about locked items, currently it swaps the item regardless of lock status, should be simple change if this wants to be avoided.

[gmiclotte]

Thanks a lot, looks nice! Sorry for the slow merge, lost track of this.