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.h

@@ -0,0 +1,10 @@
+#include <LibGUI/GSocket.h>
+
+class GTCPSocket final : public GSocket {
+public:
+    explicit GTCPSocket(GObject* parent);
+    virtual ~GTCPSocket() override;
+
+private:
+};
+