Improved/Expanded Ventcrawling

Removes the ventcrawl verb. All ventcrawlers are still ventcrawlers and can use ventcrawling with the alt click. This is simultaneously less buggy and far easier to do on the fly.

The meat of ventcrawling is now stored in the vent pump, meaning anything can ventcrawl if it has ventcrawling on.

Ventcrawling 0 is no crawling, Ventcrawling 1 is naked crawling, Ventcrawling 2 and above is always crawling.

Yes you can var edit humans to be able to ventcrawl with this, great if you want to reenact Diehard!

Simple animals that logically should fit in a vent can now ventcrawl. Note that this only is relevant for player controlled simple animals (staff of change/badminry), it won't be used by the mob AI.

Fixes #176 (FINALLY)