Blackmagic RAW in Natron

I fixed a few things on macOS that caused crashes, but it still doesn’t work.
Also I think it’s OK if you want to move the code to natrongithub.
A nice feature would be to check on plugin load if the SDK libraries are available. If not, load should fail. There’s also a lot of redundant calls to ClipOpen - maybe you could figure out a way to cache the result.

I’m not sure if we can distribute the plugin with Natron, since it requires proprietary code to run. Let’s keep it separate for now - It’s easy enough to install anyway.