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/IXWebSocketCloseConstants.cpp

@@ -0,0 +1,36 @@
+/*
+ *  IXWebSocketCloseConstants.cpp
+ *  Author: Benjamin Sergeant
+ *  Copyright (c) 2019 Machine Zone, Inc. All rights reserved.
+ */
+
+#include "IXWebSocketCloseConstants.h"
+
+namespace ix
+{
+    const uint16_t WebSocketCloseConstants::kNormalClosureCode(1000);
+    const uint16_t WebSocketCloseConstants::kInternalErrorCode(1011);
+    const uint16_t WebSocketCloseConstants::kAbnormalCloseCode(1006);
+    const uint16_t WebSocketCloseConstants::kInvalidFramePayloadData(1007);
+    const uint16_t WebSocketCloseConstants::kProtocolErrorCode(1002);
+    const uint16_t WebSocketCloseConstants::kNoStatusCodeErrorCode(1005);
+
+    const std::string WebSocketCloseConstants::kNormalClosureMessage("Normal closure");
+    const std::string WebSocketCloseConstants::kInternalErrorMessage("Internal error");
+    const std::string WebSocketCloseConstants::kAbnormalCloseMessage("Abnormal closure");
+    const std::string WebSocketCloseConstants::kPingTimeoutMessage("Ping timeout");
+    const std::string WebSocketCloseConstants::kProtocolErrorMessage("Protocol error");
+    const std::string WebSocketCloseConstants::kNoStatusCodeErrorMessage("No status code");
+    const std::string WebSocketCloseConstants::kProtocolErrorReservedBitUsed("Reserved bit used");
+    const std::string WebSocketCloseConstants::kProtocolErrorPingPayloadOversized(
+        "Ping reason control frame with payload length > 125 octets");
+    const std::string WebSocketCloseConstants::kProtocolErrorCodeControlMessageFragmented(
+        "Control message fragmented");
+    const std::string WebSocketCloseConstants::kProtocolErrorCodeDataOpcodeOutOfSequence(
+        "Fragmentation: data message out of sequence");
+    const std::string WebSocketCloseConstants::kProtocolErrorCodeContinuationOpCodeOutOfSequence(
+        "Fragmentation: continuation opcode out of sequence");
+    const std::string WebSocketCloseConstants::kInvalidFramePayloadDataMessage(
+        "Invalid frame payload data");
+    const std::string WebSocketCloseConstants::kInvalidCloseCodeMessage("Invalid close code");
+} // namespace ix