Fake physics effects to have units fly in the air after a charge/explosion nearby

[wraitii]

This is something that is wanted for charging and running, as well as a reaction to splash damage: units should go flying in the air when they receive such types of damage.

Since this is hard to simulate entirely (ragdoll physics), we could likely fake it well enough for the purposes of Part 1.

I've attached a small patch and a test map. It allows units to go flying in the air and will make them react to terrain properly (including water). However they will pass through other entities, which is the real though thing here.

The test map shows when it can be used, all units have it activated by default with the patch. Notice that if you destroy the horse on the hill, it'll slip down, and how if you shoot the woman into the water, she'll sink properly.