Menumanager: fixes (#1261)

* menumanager: 'remove' hidden entries on added

* menumanager: keep original index in mind when prio1 == prio2

runelite-api/src/main/java/net/runelite/api/Client.java

@@ -572,6 +572,12 @@ public interface Client extends GameShell
 	 */
 	void setMenuEntries(MenuEntry[] entries);
 
+	/**
+	 * Set the amount of menu entries the client has.
+	 * If you decrement this count, it's the same as removing the last one
+	 */
+	void setMenuOptionCount(int count);
+
 	/**
 	 * Checks whether a right-click menu is currently open.
 	 *