Allow dropping stash items directly and fix stacked items pickup bug
Don't drop stash items when dragging into a full inventory

Fixes #748
Check quantity in ItemStorage::full()
Fix picking up loot stacks from the ground with a full inventory
Restore old stash full checking

When trying to move items to a full stash from the inventory, we don't
have to worry about splitting the stack.
Merge pull request #749 from dorkster/menu_stash

Improvments to stash interaction