Improvements to BlockStates

* Update Javadoc of block state classes to better match implementation behaviour.
* Add Container interface which provides access to the snapshot inventory.

By: Lukas Hennig <lukas@wirsindwir.de>

paper-api/src/main/java/org/bukkit/block/ShulkerBox.java

@@ -2,12 +2,11 @@ package org.bukkit.block;
 
 import org.bukkit.DyeColor;
 import org.bukkit.Nameable;
-import org.bukkit.inventory.InventoryHolder;
 
 /**
- * Represents a ShulkerBox.
+ * Represents a captured state of a ShulkerBox.
  */
-public interface ShulkerBox extends BlockState, InventoryHolder, Lockable, Nameable {
+public interface ShulkerBox extends Container, Nameable {
 
     /**
      * Get the {@link DyeColor} corresponding to this ShulkerBox