Changed all player to AGM_Core_fnc_player.

Added altimeter, shows height ASL. Decent rate (which I'm sure I am doing wrong :D). And time.
I'm guessing it would be 100% better to have an altimeter item that needs to be an assignedItem. Will cover that next.

https://github.com/KoffeinFlummi/AGM/issues/540
Oh. The descent rate is marked as m/min on the altimeter. In that case:

`_descentRate = (_oldHeight - _height) / (_time - _oldTime) * 60;`