SPIGOT-3246: Use Sittable for Ocelot, Wolf and Parrot

By: BlackHole <black-hole@live.com>

paper-api/src/main/java/org/bukkit/entity/Sittable.java

@@ -0,0 +1,23 @@
+package org.bukkit.entity;
+
+/**
+ * An animal that can sit still.
+ */
+public interface Sittable {
+
+    /**
+     * Checks if this animal is sitting
+     *
+     * @return true if sitting
+     */
+    boolean isSitting();
+
+    /**
+     * Sets if this animal is sitting. Will remove any path that the animal
+     * was following beforehand.
+     *
+     * @param sitting true if sitting
+     */
+    void setSitting(boolean sitting);
+
+}