Prefix server logs

Sometimes, it is not obvious whether a log is generated by the server or
by the client. Prefix server logs for clarity.

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

@@ -9,6 +9,7 @@ import android.util.Log;
 public final class Ln {
 
     private static final String TAG = "scrcpy";
+    private static final String PREFIX = "[server] ";
 
     enum Level {
         DEBUG,
@@ -30,28 +31,28 @@ public final class Ln {
     public static void d(String message) {
         if (isEnabled(Level.DEBUG)) {
             Log.d(TAG, message);
-            System.out.println("DEBUG: " + message);
+            System.out.println(PREFIX + "DEBUG: " + message);
         }
     }
 
     public static void i(String message) {
         if (isEnabled(Level.INFO)) {
             Log.i(TAG, message);
-            System.out.println("INFO: " + message);
+            System.out.println(PREFIX + "INFO: " + message);
         }
     }
 
     public static void w(String message) {
         if (isEnabled(Level.WARN)) {
             Log.w(TAG, message);
-            System.out.println("WARN: " + message);
+            System.out.println(PREFIX + "WARN: " + message);
         }
     }
 
     public static void e(String message, Throwable throwable) {
         if (isEnabled(Level.ERROR)) {
             Log.e(TAG, message, throwable);
-            System.out.println("ERROR: " + message);
+            System.out.println(PREFIX + "ERROR: " + message);
             if (throwable != null) {
                 throwable.printStackTrace();
             }