Implemented ShouldRenderPassEvent for all entities

This change adds the possibility of modifying the renderpass of a piece of armor to every entity that wears armor. As long as they implement this event.

Added the event to Biped entities as an example and an actual addition, cause my initial PR #1392 was just for this purpose.

After some discussions on IRC I decided to make the event general so that it could be reused for the 1.8 Armorstands. Once there is a branch on 1.8 i will make a PR for that to implement it properly.

I also marked RenderPlayerEvent.setArmorModel as Deprecated as it is completely replaced with this event that has the same functionality. On said upcoming PR for 1.8 i will also remove that event completely from the code, giving people time to adapt if they are depending on it, and cleaning up that bid of redundant code.

During said discussion on IRC no one seemed to know were the name setArmorModel came from, after looking through the history of that class I could not find the person who implemented it so after some thinking i also renamed named the event to a more understandable one: ShouldRenderPassEvent.

I also added a description to the event as that was not available for the setArmorModel one. It explains what is possible with this powerful rendering event.
There is no reason to continue to fire the old event, cause i am going to delete it anyway. See initial comment. The task i got was to create an general system that could be used for instances were this was required. Leaving the event in place would just create redundant code.

But if there is enough anymo for it will continue to fire it and replace it on the upcoming 1.8 commit once the branch for it is there.