Fix client crash when preview_cb is nil.

Fix potential crash.

- Add support for fully automatic animal tracking for lag compensation disabled client.

1. Now you can just press F2 (shortcut key) to activate the dirt pile.
2. Remove mole_move_fx after it's spawned.

Fixed hotkey configuration mistake.

Now added helper for lost toys!

When the cute pipspook has radar animation above his/her head, you can press F11 (default) to go directly to the lost toys.

Pressing the shortcut key before joining a server will not crash the game anymore.

Now supports Lag Compensation and Non-cave servers.

Thanks @JKstring for making this possible.

Added shortcut key (default is F2, configurable in options) to follow the Animal Track even easier.