Shocking animations

![shocked](https://cloud.githubusercontent.com/assets/5659269/5426450/dfdb3f5e-831f-11e4-9fab-d5ad06aaad16.gif)
Adds animations for being shocked. Affected mobs will convulse for a moment before falling down. After collapsing, the stun will have its normal duration - shocked mobs will also shake around a bit after falling.
Can you remove this from under the spawn? I'd like it to return that value straight away, as opposed to after 20 ticks, it may cause it to return null (the default) and then shock_damage