Add Skull BlockState and Type enum. Adds BUKKIT-3258

By: meiskam <meiskam@gmail.com>

paper-api/src/main/java/org/bukkit/SkullType.java

@@ -0,0 +1,12 @@
+package org.bukkit;
+
+/**
+ * Represents the types of skulls
+ */
+public enum SkullType {
+    SKELETON,
+    WITHER,
+    ZOMBIE,
+    PLAYER,
+    CREEPER;
+}

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

@@ -0,0 +1,59 @@
+package org.bukkit.block;
+
+import org.bukkit.SkullType;
+
+/**
+ * Represents a Skull
+ */
+public interface Skull extends BlockState {
+
+    /**
+     * Checks to see if the skull has an owner
+     *
+     * @return true if the skull has an owner
+     */
+    public boolean hasOwner();
+
+    /**
+     * Gets the owner of the skull
+     *
+     * @return the owner if the skull
+     */
+    public String getOwner();
+
+    /**
+     * Sets the owner of the skull
+     *
+     * @param owner the new owner of the skull
+     * @return true if the owner was successfully set
+     */
+    public boolean setOwner(String name);
+
+    /**
+     * Gets the rotation of the skull
+     *
+     * @return the rotation of the skull
+     */
+    public BlockFace getRotation();
+
+    /**
+     * Sets the rotation of the skull
+     *
+     * @param rotation the rotation of the skull
+     */
+    public void setRotation(BlockFace rotation);
+
+    /**
+     * Gets the type of skull
+     *
+     * @return the type of skull
+     */
+    public SkullType getSkullType();
+
+    /**
+     * Sets the type of skull
+     *
+     * @param skullType the type of skull
+     */
+    public void setSkullType(SkullType skullType);
+}