Change: base autosaves intervals on real time (instead of game time) (#10655)

There are two fundamental issues with autosave:
- When fast-forwarding, it saves way too often
- When paused, it never saves

Both makes no sense. Autosaves are meant to prevent you from
accidentally losing your work. The emphasis on "your" work.

To solve both issues, the autosave now works on real time. You
can select every 10 / 30 / 60 / 120 minutes, which are similar to
what the setting was in game-months.

When you pause, autosaving will stop. Unless you make any change
to the game; then it will continue to make autosaves, even so
the game is paused. Unpausing / pausing resets this mechanism.

src/misc_cmd.cpp

@@ -173,6 +173,11 @@ CommandCost CmdPause(DoCommandFlag flags, PauseMode mode, bool pause)
 				_pause_mode |= mode;
 			} else {
 				_pause_mode &= ~mode;
+
+				/* If the only remaining reason to be paused is that we saw a command during pause, unpause. */
+				if (_pause_mode == PM_COMMAND_DURING_PAUSE) {
+					_pause_mode = PM_UNPAUSED;
+				}
 			}
 
 			NetworkHandlePauseChange(prev_mode, mode);