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/httpd.cpp

@@ -0,0 +1,46 @@
+/*
+ *  httpd.cpp
+ *  Author: Benjamin Sergeant
+ *  Copyright (c) 2020 Machine Zone, Inc. All rights reserved.
+ *
+ *  Buid with make httpd
+ */
+
+#include <ixwebsocket/IXHttpServer.h>
+#include <sstream>
+#include <iostream>
+
+int main(int argc, char** argv)
+{
+    if (argc != 3)
+    {
+        std::cerr << "Usage: " << argv[0]
+                  << " <port> <host>" << std::endl;
+        std::cerr << " " << argv[0] << " 9090 127.0.0.1" << std::endl;
+        std::cerr << " " << argv[0] << " 9090 0.0.0.0" << std::endl;
+        return 1;
+    }
+
+    int port;
+    std::stringstream ss;
+    ss << argv[1];
+    ss >> port;
+    std::string hostname(argv[2]);
+
+    std::cout << "Listening on " << hostname
+              << ":" << port << std::endl;
+
+    ix::HttpServer server(port, hostname);
+
+    auto res = server.listen();
+    if (!res.first)
+    {
+        std::cout << res.second << std::endl;
+        return 1;
+    }
+
+    server.start();
+    server.wait();
+
+    return 0;
+}