ColorManager is now specific to the Project

OCIO config was set on a per-project basis, but we were using a singleton for
the ColorManager that would break if more than one project was ever open.
Now the ColorManager belongs to the Project and is always accessed through the
Project.

app/core.cpp

@@ -99,9 +99,6 @@ void Core::Start()
   // Load application config
   Config::Load();
 
-  // Set up color manager
-  ColorManager::CreateInstance();
-
 
   //
   // Start GUI (FIXME CLI mode)
@@ -121,8 +118,6 @@ void Core::Stop()
 
   AudioManager::DestroyInstance();
 
-  ColorManager::DestroyInstance();
-
   NodeFactory::Destroy();
 
   delete main_window_;