Add building blocks for asio implementation

• vtkAsioInternalsConnection wraps asio::async_read and asio::async_write from or to an asio::ip::tcp::socket
• vtkAsioInternalsSharedConstBuffer is an implementation detail to keep the data alive until an async_write operation completes.
• vtkAsioInternalsClient can connect to a compatible server that transmits a service registry upon connection.
• vtkAsioInternalsServer can accept connections from any client. Upon accepting a connection, it immediately transmits a service registry. It's HandleRead method is setup to read asynchronously from the connection forever until the client disconnects.
• vtkAsioInternalsServiceRegistry has some functions and types that may not make immediate sense. However, it helps the TestAsioInternals program.
• vtkAsioInternalsTestUtility is the public entry point for the TestAsioInternals program to use asio for emulating a builtin session for now.