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/overlaycontroller.cpp

@@ -118,7 +118,7 @@ OverlayController::OverlayController( bool desktopMode,
             nullptr, "OpenVR Advanced Settings Overlay", "Is OpenVR running?" );
         throw std::runtime_error( std::string( "No Overlay interface" ) );
     }
-
+    m_actions.Init( false );
     // Init controllers
     m_steamVRTabController.initStage1();
     m_chaperoneTabController.initStage1();
@@ -477,6 +477,13 @@ void OverlayController::OnTimeoutPumpEvents()
     if ( !vr::VRSystem() )
         return;
 
+    m_actions.Loop();
+
+    if ( m_actions.nextSongSet() )
+    {
+        LOG( INFO ) << "NEXT SONG SET!";
+    }
+
     vr::VREvent_t vrEvent;
     bool chaperoneDataAlreadyUpdated = false;
     while ( pollNextEvent( m_ulOverlayHandle, &vrEvent ) )