Implement NetworkManager

For now there are two methods:

- `NETWORK:IsUrlAllowed()`: Check whether access to a certain URL is allowed.
- `NETWORK:HttpRequest()`: Perform an HTTP request.

By default access to the network is disabled for all target hosts. It
can be enabled by setting `HttpEnable=1` in the preferences. Individual
hosts have to be added to `HttpAllowHosts` as a comma separated list to
allow access.

See included docs for more details on usage.

extern/IXWebSocket-11.3.2/ixwebsocket/IXUserAgent.cpp

@@ -0,0 +1,89 @@
+/*
+ *  IXUserAgent.cpp
+ *  Author: Benjamin Sergeant
+ *  Copyright (c) 2017-2019 Machine Zone, Inc. All rights reserved.
+ */
+
+#include "IXUserAgent.h"
+
+#include "IXWebSocketVersion.h"
+#include <sstream>
+#ifdef IXWEBSOCKET_USE_ZLIB
+#include <zlib.h>
+#endif
+
+// Platform name
+#if defined(_WIN32)
+#define PLATFORM_NAME "windows" // Windows
+#elif defined(_WIN64)
+#define PLATFORM_NAME "windows" // Windows
+#elif defined(__CYGWIN__) && !defined(_WIN32)
+#define PLATFORM_NAME "windows" // Windows (Cygwin POSIX under Microsoft Window)
+#elif defined(__ANDROID__)
+#define PLATFORM_NAME "android" // Android (implies Linux, so it must come first)
+#elif defined(__linux__)
+#define PLATFORM_NAME "linux" // Debian, Ubuntu, Gentoo, Fedora, openSUSE, RedHat, Centos and other
+#elif defined(__unix__) || !defined(__APPLE__) && defined(__MACH__)
+#include <sys/param.h>
+#if defined(BSD)
+#define PLATFORM_NAME "bsd" // FreeBSD, NetBSD, OpenBSD, DragonFly BSD
+#endif
+#elif defined(__hpux)
+#define PLATFORM_NAME "hp-ux" // HP-UX
+#elif defined(_AIX)
+#define PLATFORM_NAME "aix"                   // IBM AIX
+#elif defined(__APPLE__) && defined(__MACH__) // Apple OSX and iOS (Darwin)
+#include <TargetConditionals.h>
+#if TARGET_IPHONE_SIMULATOR == 1
+#define PLATFORM_NAME "ios" // Apple iOS
+#elif TARGET_OS_IPHONE == 1
+#define PLATFORM_NAME "ios" // Apple iOS
+#elif TARGET_OS_MAC == 1
+#define PLATFORM_NAME "macos" // Apple OSX
+#endif
+#elif defined(__sun) && defined(__SVR4)
+#define PLATFORM_NAME "solaris" // Oracle Solaris, Open Indiana
+#else
+#define PLATFORM_NAME "unknown platform"
+#endif
+
+// SSL
+#ifdef IXWEBSOCKET_USE_MBED_TLS
+#include <mbedtls/version.h>
+#elif defined(IXWEBSOCKET_USE_OPEN_SSL)
+#include <openssl/opensslv.h>
+#endif
+
+namespace ix
+{
+    std::string userAgent()
+    {
+        std::stringstream ss;
+
+        // IXWebSocket Version
+        ss << "ixwebsocket/" << IX_WEBSOCKET_VERSION;
+
+        // Platform
+        ss << " " << PLATFORM_NAME;
+
+        // TLS
+#ifdef IXWEBSOCKET_USE_TLS
+#ifdef IXWEBSOCKET_USE_MBED_TLS
+        ss << " ssl/mbedtls " << MBEDTLS_VERSION_STRING;
+#elif defined(IXWEBSOCKET_USE_OPEN_SSL)
+        ss << " ssl/OpenSSL " << OPENSSL_VERSION_TEXT;
+#elif __APPLE__
+        ss << " ssl/SecureTransport";
+#endif
+#else
+        ss << " nossl";
+#endif
+
+#ifdef IXWEBSOCKET_USE_ZLIB
+        // Zlib version
+        ss << " zlib " << ZLIB_VERSION;
+#endif
+
+        return ss.str();
+    }
+} // namespace ix