Implement beta IVRInput system for testing

In order to test new system:

Build and deploy application.

Copy both files from IVRInput/ dir into the bin/win64 folder.

Change const std::string m_actionManifestPath in steamivrinput.h to be
directly to your action_manifest.json file.

Run and turn on a Vive controller. Press the menu button. If logs say
"NEXT SONG SET!" it works.

src/steamivrinput.h

@@ -0,0 +1,22 @@
+#ifndef STEAMIVRINPUT_H
+#define STEAMIVRINPUT_H
+
+#include <openvr.h>
+
+class SteamIVRInput
+{
+public:
+    void Init( const bool init );
+    void Loop();
+    bool nextSongSet();
+
+private:
+    const std::string m_actionManifestPath
+        = "YOUR_PATH_HERE\\action_manifest.json";
+    vr::VRActionHandle_t m_nextSongHandler = {};
+    vr::VRActionSetHandle_t m_mainSetHandler = {};
+    vr::VRActiveActionSet_t m_activeActionSet = {};
+    vr::InputDigitalActionData_t m_nextSongData = {};
+};
+
+#endif // STEAMIVRINPUT_H