Introduce ServerConnection interface

This will become very useful for plugin messaging support.

api/src/main/java/com/velocitypowered/api/proxy/Player.java

@@ -29,7 +29,7 @@ public interface Player extends CommandSource, InboundConnection {
      * Returns the server that the player is currently connected to.
      * @return an {@link Optional} the server that the player is connected to, which may be empty
      */
-    Optional<ServerInfo> getCurrentServer();
+    Optional<ServerConnection> getCurrentServer();
     
     /**
      * Sends a chat message to the player's client.

api/src/main/java/com/velocitypowered/api/proxy/ServerConnection.java

@@ -0,0 +1,12 @@
+package com.velocitypowered.api.proxy;
+
+import com.velocitypowered.api.server.ServerInfo;
+
+/**
+ * Represents a connection to a backend server from the proxy for a client.
+ */
+public interface ServerConnection {
+    ServerInfo getServerInfo();
+
+    Player getPlayer();
+}