Add bunch of knockback fixes

[furudee]

Fixes #1431
This request does a few things:

1. Makes WorldData.GetAllActorsTrace a line trace by commenting out Extents, since it often got stuck on ground, curbs and other floor tiles. I assume the logic was that units cannot be knocked down from buildings and other high places
2. Units may now take fall damage from falling from such high places, and units landed on take damage. After whatever gamestate the knockback is in, I create a delegate to make a new falling gamestate to deal with the falling action.
3. Units may fly over other units and land on them, if they're high enough to take fall damage. Before it ended and set the knockback location before the unit you're flying over.
4. Adds custom visualization tree merging logic when fall is triggered by a knockback. This removes the X2Action_Falling node from the build tree, since otherwise the unit will "fall down" twice. A normal falling context caused by destruction of floor beneath the unit shouldn't end up at the newly added segment, but I'm not certain

And since it's a quite large fix, I would like it to be tested more

[Iridar]

Looks very intriguing, I can't really follow the code, so we'll just have to do some extensive testing.

[BlackDog86]

Hmm, weird that it's not linking the issue and the PR

Can you try just Fixes #XXXX instead of Fixes Issue #XXXX in the first comment?