LiveData: Initial implementation

Add support for live data subscription via Device::subscribeLiveData() and
Device::unsubscribeLiveData(). The live data API can be used to subscribe to
individual "signals", a full list of which can be found in LiveDataValueType.

communication/message/livedatamessage.cpp

@@ -0,0 +1,15 @@
+#include "icsneo/communication/message/livedatamessage.h"
+#include "icsneo/communication/livedata.h"
+
+namespace icsneo
+{
+
+void LiveDataCommandMessage::appendSignalArg(LiveDataValueType valueType) {
+	auto& arg = args.emplace_back(std::make_shared<LiveDataArgument>());
+	arg->objectType = LiveDataObjectType::MISC;
+	arg->objectIndex = 0u;
+	arg->signalIndex = 0u;
+	arg->valueType = valueType;
+}
+
+} // namespace icsneo