Initial Netty implementation for networking

Split into 1 LoginServer and 1 ChannelServer per channel.

There is still a lot of cleanup and refactoring to be done.
Currently, the reliance on IoSession holding client state
is the most pressing issue to be addressed.

src/main/java/net/netty/ChannelServer.java

@@ -0,0 +1,40 @@
+package net.netty;
+
+import io.netty.bootstrap.ServerBootstrap;
+import io.netty.channel.Channel;
+import io.netty.channel.EventLoopGroup;
+import io.netty.channel.nio.NioEventLoopGroup;
+import io.netty.channel.socket.nio.NioServerSocketChannel;
+
+public class ChannelServer extends AbstractServer {
+    private final int world;
+    private final int channel;
+    private Channel nettyChannel;
+
+    public ChannelServer(int port, int world, int channel) {
+        super(port);
+        this.world = world;
+        this.channel = channel;
+    }
+
+    @Override
+    public void start() {
+        EventLoopGroup parentGroup = new NioEventLoopGroup();
+        EventLoopGroup childGroup = new NioEventLoopGroup();
+        ServerBootstrap bootstrap = new ServerBootstrap()
+                .group(parentGroup, childGroup)
+                .channel(NioServerSocketChannel.class)
+                .childHandler(new ChannelServerInitializer(world, channel));
+
+        this.nettyChannel = bootstrap.bind(port).syncUninterruptibly().channel();
+    }
+
+    @Override
+    public void stop() {
+        if (nettyChannel == null) {
+            throw new IllegalStateException("Must start ChannelServer before stopping it");
+        }
+
+        nettyChannel.close().syncUninterruptibly();
+    }
+}