Add empty web.xml in order to prevent DWR warnings

Fixes #1255

airsonic-main/src/main/webapp/WEB-INF/web.xml

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="ISO-8859-1"?>
+<web-app version="3.0" xmlns="http://java.sun.com/xml/ns/javaee"
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
+	https://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
+	<!--
+	The Airsonic Spring configuration is annotation-based.
+	This file is kept empty in order to prevent DWR from emitting warnings.
+
+	See: https://github.com/airsonic/airsonic/issues/1255
+	-->
+</web-app>