Fixed stairs & chests rendering

-Fixed chests rendering in inventory (kinda).
-Fixed stairs rendering.
From now on, all blocks with multiple states MUST have item model.
Example stair provided (though with incorrect textures).
Relates to #9.

src/main/java/appeng/block/AEBaseStairBlock.java

@@ -33,7 +33,7 @@ import appeng.core.features.IAEFeature;
 import appeng.core.features.IFeatureHandler;
 
 
-public abstract class AEBaseStairBlock extends BlockStairs implements IAEFeature
+public abstract class AEBaseStairBlock extends BlockStairs implements IAEFeature, IHasSpecialItemModel
 {
 	private final IFeatureHandler features;