Add goal net movement on ball impact

[Aryan14]

The goal net should move when the ball hits it.

There are two possible approaches for this:

1. Ragdoll

   Create a ragdoll skeleton in a modelling program which reacts to collision according to the Source engine's physics engine, similar to the mattress model or a dead player's model in the various Source games.

   Pro:

   • The collision mesh moves with the impacting ball, so the behavior should look fairly realistic.

   Con:

   • Possibly expensive (although FPS dips shouldn't be as much of a problem, since ball/net collision only happens when the ball is no longer in the game, therefore not affecting players' performances)
   • Can only have a couple of collision mesh parts, thus making it hard to have realistic looking dents in the net on impact.

2. Shader

   Write a vertex shader which moves the net vertices on ball impact.

   Pro:

   • Can produce much more realistic looking net movement effects than the ragdoll

   Con:

   • How to make the ball move with the net vertices, instead of passing through the net or bouncing of a collision box