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
Yep, you're doing this wrong. Should be something like: 

`_descentRate = (_oldHeight - _height) / (_time - _oldTime);`

or if you are feeling lazy:

`_descentRate = (_oldHeight - _height) / 0.2;`