Support player's inventory, container and companion windows with
dropping and picking up items from the world.
Add ItemTransfer class to handle transfers similar to DragAndDrop. When
a container window is opened the view is added to the set of targets and
removed when closed. If ALT is pressed instead of starting dragging an
item perform a transfer. If there is 1 target which is not a source move
item there. If there is no target drop item into the world using
WorldItemModel.
Special case is picking up an item. Don't start dragging, just update
the player's inventory view because the item is already there.
Kept some fixes from the first round of review. Found out that several
targets weren't being built with the same basic warnings disabled.
Disabled a few warnings for external libraries specifically, rather than
applying them to all targets.
