Padlock mechanic

[elliot-nelson]

Implement short (4-5 number) "padlock entry". Preferably possible just with arrow keys, and not requiring number keys, to increase future portability.

("Number entry" allows us the option to have clues the player must actually read, refer to, and enter manually, which is a different mechanic than just picking one of the items you are carrying repeatedly and trying to use it. It also allows for the possibility of rudimentary math puzzles, or logic puzzles where the output is a number.)