Apply upstream improvement to access mappings in-game (commit:c67d4b5)

Another merge of an [upstream commit](https://github.com/Arcnor/pixel-dungeon-gdx/commit/c67d4b5bff446c61ad875638f665724260e9b404) pushed by @watabou, this time enabling the ability to set key bindings from the settings menu in-game (as opposed to only at the title screen).