made openvr opt-in

CMakeLists.txt

 cmake_minimum_required(VERSION 3.0)
 project(LavaExtras)
 
+option(LAVA_EXTRAS_OPENVR "enable support for OpenVR in lava-extras" OFF)
+
 find_package(Boost)
 
 add_subdirectory(camera)
@@ -9,5 +11,8 @@ add_subdirectory(glfw)
 add_subdirectory(renderer)
 add_subdirectory(pack)
 add_subdirectory(geometry)
-add_subdirectory(openvr)
 add_subdirectory(glsl)
+
+if (LAVA_EXTRAS_OPENVR)
+    add_subdirectory(openvr)
+endif()