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/IXExponentialBackoff.cpp

@@ -0,0 +1,31 @@
+/*
+ *  IXExponentialBackoff.cpp
+ *  Author: Benjamin Sergeant
+ *  Copyright (c) 2017-2019 Machine Zone, Inc. All rights reserved.
+ */
+
+#include "IXExponentialBackoff.h"
+
+#include <cmath>
+
+namespace ix
+{
+    uint32_t calculateRetryWaitMilliseconds(uint32_t retryCount,
+                                            uint32_t maxWaitBetweenReconnectionRetries,
+                                            uint32_t minWaitBetweenReconnectionRetries)
+    {
+        uint32_t waitTime = (retryCount < 26) ? (std::pow(2, retryCount) * 100) : 0;
+
+        if (waitTime < minWaitBetweenReconnectionRetries)
+        {
+            waitTime = minWaitBetweenReconnectionRetries;
+        }
+
+        if (waitTime > maxWaitBetweenReconnectionRetries || waitTime == 0)
+        {
+            waitTime = maxWaitBetweenReconnectionRetries;
+        }
+
+        return waitTime;
+    }
+} // namespace ix