Various fixes/additions.

- Close Backpack when open if you hit the open key (toggle now).
- Execute one last save run on shutdown (but only if it wasn't already
  running).
- Implement logging of inventory clicks. Every action is logged and
  handled correctly: only clicks of empty slots are ignored (which is
  safe).
- Clear and close any Backpack windows in-which an admin has deleted their
  backpack but the user had the window open in the process (race
  condition). To prevent an exploit, I clear their clicked item and
  immeadtedly close the window. This needs more testing.
- Allow lowercase naming of sizes within backpack files.

Signed-off-by: Chris Sanders <zidane@outlook.com>