Introduced the ViewportController that sits between the application and the Scene2D to handle the trackers and measuring tools. This is a work in progress. The Scene2D is no longer an observable. Message sending is managed by the ViewportController. Move some refs to shared and weak to prevent lifetime issues.

#pragma once

#if ORTHANC_ENABLE_WASM == 1
// https://emscripten.org/docs/optimizing/Optimizing-WebGL.html
#  define ORTHANC_STONE_OPENGL_SHADER_VERSION_DIRECTIVE "precision mediump float;\n"
#else
#  define ORTHANC_STONE_OPENGL_SHADER_VERSION_DIRECTIVE "#version 110\n"
#endif