Use two sockets for video and control

The socket used the device-to-computer direction to stream the video and
the computer-to-device direction to send control events.

Some features, like copy-paste from device to computer, require to send
non-video data from the device to the computer.

To make them possible, use two sockets:
 - one for streaming the video from the device to the client;
 - one for control/events in both directions.

server/src/main/java/com/genymobile/scrcpy/Server.java

@@ -24,7 +24,7 @@ public final class Server {
 
             try {
                 // synchronous
-                screenEncoder.streamScreen(device, connection.getFd());
+                screenEncoder.streamScreen(device, connection.getVideoFd());
             } catch (IOException e) {
                 // this is expected on close
                 Ln.d("Screen streaming stopped");