Missing deinterlace options

[JRB-Prod]

Hi, what a nice plugin! I only noticed that OBS is unfortunately not able to add deinterlace options to the right click menu by default. I was eventually able to find something in the source code that says this is only possible if the video source output_flags has the OBS_SOURCE_ASYNC flag set. I don't know exactly what the best / prettiest way is to add this functionality to the plugin, but I have at least created something myself that seems to work. It adds two additional lists from which you can set the deinterlace mode and field order. I haven't made a pull request because I'm not yet sure of the best approach. For now I'll have to keep using my own fork because I really need this functionality.