Improvements to tent save/load and debugging code

Added debug labels to tents.

Tent item indexing is now improved a little more. However, items can
only be added to tents by dropping them (CreateItemInWorld calls don't
work any more) because it uses OnPlayerDroppedItem and
GetPlayerButtonList to determine which tent to add the item to (the
closest one) efficiently.

Added dev commands for toggling SIF debug labels.