WebServer: Move server configuration into WebServer::Configuration

This moves the configuration of the web server, which currently only
consists of the root path, into a new class, Configuration. Since the
configuration is global and not per client, it is accessed by a
singleton getter.

This change simplifies future extensions of the configurable parameters.

Userland/Services/WebServer/Configuration.cpp

@@ -0,0 +1,26 @@
+/*
+ * Copyright (c) 2021, Max Wipfli <mail@maxwipfli.ch>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <WebServer/Configuration.h>
+
+namespace WebServer {
+
+static Configuration* s_configuration = nullptr;
+
+Configuration::Configuration(String root_path)
+    : m_root_path(move(root_path))
+{
+    VERIFY(!s_configuration);
+    s_configuration = this;
+}
+
+Configuration const& Configuration::the()
+{
+    VERIFY(s_configuration);
+    return *s_configuration;
+}
+
+}