PLR Cart Elevator Prefab A3b

Fixes:

* The mid-path elevator prefab did not work at all.
* The mid-path elevator cart would not continue after leaving the elevator until players re-entered the push zone.

Fixed issue where the blue cart couldn't be blocked by red. This requires a team_control_point_round despite being single stage, so don't remove it!

Stopped the mid-track elevator from rising while the cart is pushed after leaving it.

* The mid-track elevator now falls back down once the cart has left.