Weight penalty improvements

The current weight penalties were too much due to me failing to take into account pain effects on weight limits. This PR:
* Greatly reduces pain penalty chances for weights
* Adds pain caps based on how overburdened you are
* Halves overburdened speed penalty (with the weight rework's pain penalty this makes it about equal to before the rework)
* Causes the player to collapse to the ground if they are carrying too much (4x their maximum) until they drop some stuff.

Fixes issue #2489.