Ensured debug mode key handlers always exist

Before this commit the debug console's key handler wasn't added to saved games which didn't have it because they weren't started with debugging enabled and the debug script's key handler would
only be added to saved games older than 85 when debugging was enabled. So if debugging was enabled for a saved game newer than 85 the key handler for the debug script would be missing.
@TheCycoONE UI:addOrRemoveDebugModeKeyHandlers() removes them but then adds them again when debugging is enabled to make sure duplicate table entries aren't added.