The ViewerGLWidget would receive raw GLuint textures while most of Olive uses
an OpenGLTexture C++ wrapper. Unfortunately this would lead to the C++ wrapper
getting destroyed since its instance wasn't kept in the ViewerGLWidget. This
meant by the time the ViewerGLWidget would re-draw, the texture would have
already been destroyed leading to some black frames. This is now fixed.
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.
The viewer had the color management backend in place already, but the frontend
was non-functional. This commit implements most if not all color management
functionality.