Move OpenVR init function out of Overlaycontroller

This prevents the issue of OpenVR not being initialized in constructors
of other objects, and there's really no reason not to do it.

src/main.cpp

@@ -37,6 +37,9 @@ int main( int argc, char* argv[] )
                                    commandLineArgs.forceRemoveManifest );
     }
 
+    openvr_init::OpenVR_Init openvr_init(
+        openvr_init::OpenVrInitializationType::Overlay );
+
     try
     {
         // QSettings contains a platform independant way of storing settings in