small UI things about v.264

[McGuffin]

First of all, as always, very nice update, I love the game more and more each time.

Here are few very minor (UI) details that could be improved , imho:

- In the save slot selection, show the game difficulty.

- The holster key (H by default) could remember what was the last used object, so it can quickly be used as a toggle item on /off