Used AddMixingTransform to blend punch and shoot animations with walk/run.

* Added `layer` and `blendMode` properties to the `punch` and `shoot` anims in
  `SideScrollCharacterAnimation.js`. Also utilize the `AddMixingTransform()`
  function in order to add a mixed animation on the `torso` in order to mix the
  animations with the walk and run cycles.
* Removed the restrictions on the punch and shoot animations in order to allow
  punching and shooting while walking/jumping/etc.
* Deleted unused file, `testScene`