Refactor IVRInput logic into several classes

Keeping the action name, handle and type together allows for better
error messages and limited run time type checking, to ensure that the
wrong function isn't called.

It is necessary to initialize the manifest in a class, since the Actions
depend on this being set.

Several files have been moved around to be more consistent.

src/overlaycontroller/openvr_init.cpp

@@ -70,6 +70,10 @@ OpenVR_Init::OpenVR_Init()
     {
         reportVersionError( vr::IVRNotifications_Version );
     }
+    else if ( !vr::VR_IsInterfaceVersionValid( vr::IVRInput_Version ) )
+    {
+        reportVersionError( vr::IVRInput_Version );
+    }
 }
 
 OpenVR_Init::~OpenVR_Init()