ocio looks menu doesn't allow to enable more than one look

Some of our shows have OCIO configurations where we split a _shot_ look from a _show_ look. Both need to be enabled for the final image. This is possible in OCIO by applying a look transform with the value "shot,show".

In OpenRV's OCIO menu, however, looks are exclusive: you can enable a look (a checkmark appears) but if you click the menu entry for another look the first one gets disabled again. I can, however, apply two looks in my custom rv_ocio_setup.py file. Ours is based on RV's example code and I can return an OCIOLook node with a value of "shot,show" for the ocio_look.look parameter and both looks will be applied.

Expectation:

Checkmarks on both "shot" and "show" in the OCIO menu's look submenu if "shot,show" is enabled.

What happens instead:

The OCIO menu will not show checkmarks for _any_ of its look entries.

Ideas:

- in its most simple form, this could be fixed by not making the look entries exclusive checkmarks.
- alternatively, when a look definition like "lookA,lookB" is defined by rv_ocio_setup.py the menu could add this as another option in the look submenu, allowing the menu's checkmarks to remain exclusive toggles. The user, however, would now be able to choose either lookA or lookB or both at the same time.

No file or test is named in the issue. Start by locating the OpenColorIO looks menu entry point, reproduce a configuration using "shot,show", and verify that the menu reflects both enabled looks with checkmarks.

Written by the indexing model from the issue text.