Double chests

This adds all the functionality for double chests:
- correct facing
- correct inventory (loading/saving)

The problem that currently exists is that Bukkit doesn't have MaterialData for TRAPPED_CHESTS. I added TRAPPED_CHEST as BlockChest too, since I assume that TRAPPED_CHESTS should also have a MaterialData of org.bukkit.material.Chest. If this is added to Glowkit it should automatically work with trapped chests correct, but since then placing trapped_chests gives you a warning in the console.
(See: [GlowkitPR]( https://github.com/GlowstoneMC/Glowkit/pull/23)
 
Fixes #263 
Fixes #329