OCIO Colorspace Errors

[beatreichenbach]

Several parts of the tool rely on being able to convert images to different colorspaces.

Currently the user just gets a warning hidden away in the logger:

DisplayViewTransform error. Cannot find source color space named 'Utility - XYZ - D60'.

Additional OCIO improvements:

• [x] Investigate whether it's possible to do some of the colorspace conversions on the GPU as they are really slow on the CPU.
• [x] Add control for OCIO view transforms on the viewers (qt-extension repository).
• [x] Convert output to ACEScg before the image hits the viewer. Keeping the rendering space in ACEScg makes more sense as it's also needed for the image based renderer #53.

[beatreichenbach]

Unfortunately it seems like the GPU can only realistically be used with OpenGL. For now v0.4.4 is converting the image to acescg on the GPU. This means only the viewer needs to convert the image on the CPU.

[beatreichenbach]

Finally added Display View settings in the settings menu. It applies for all viewers for now but it's okay enough for now.