Added several events required for stereoscopic rendering of the ingame world

notable changes are in Minecraft.java and EntityRenderer.java

There are only ClientSide changes.

Events were created so that a class can register for them (using @ForgeSubscribe). 
2 @Cancelable events added to prevent unwanted chunk updates and buffer manipulation. 

Hooks are initially used in this project: 
https://github.com/zsawyer/Stereoscopic3D-for-Minecraft
![minecraft-Stereoscopic3D-SideBySide_01](https://f.cloud.github.com/assets/897208/169672/b5bb8a34-7a30-11e2-8545-9b272f0dbac3.png)
![minecraft-Stereoscopic3D-interlaced_3](https://f.cloud.github.com/assets/897208/169676/d9db6628-7a30-11e2-9ac9-0da68bb19708.png)