LibGUI: Add GTCPSocket and base class GSocket (inherits from GIODevice.)

And use these to do the line-by-line reading automagically instead of having
that logic in IRCClient. This will definitely come in handy.

LibGUI/GTCPSocket.cpp

@@ -0,0 +1,19 @@
+#include <LibGUI/GTCPSocket.h>
+#include <sys/socket.h>
+
+GTCPSocket::GTCPSocket(GObject* parent)
+    : GSocket(GSocket::Type::TCP, parent)
+{
+    int fd = socket(AF_INET, SOCK_STREAM, 0);
+    if (fd < 0) {
+        set_error(fd);
+    } else {
+        set_fd(fd);
+        set_mode(GIODevice::ReadWrite);
+        set_error(0);
+    }
+}
+
+GTCPSocket::~GTCPSocket()
+{
+}