Allow Entities to be CommandSenders and add ProxiedCommandSender

By: Thinkofdeath <thinkofdeath@spigotmc.org>

paper-api/src/main/java/org/bukkit/command/ProxiedCommandSender.java

@@ -0,0 +1,20 @@
+
+package org.bukkit.command;
+
+public interface ProxiedCommandSender extends CommandSender {
+
+    /**
+     * Returns the CommandSender which triggered this proxied command
+     *
+     * @return the caller which triggered the command
+     */
+    CommandSender getCaller();
+
+    /**
+     * Returns the CommandSender which is being used to call the command
+     *
+     * @return the caller which the command is being run as
+     */
+    CommandSender getCallee();
+
+}