Add Chroma Key option to OSD Overlay

[Knifa]

Few folks have been asking for this! 🚀

Just skips blitting the video frame basically and does a magenta background instead.

Still runs off the DVR video for timing, etc., etc. Could improve this later to generate from the OSD files directly.

[Knifa]

Admittedly a bit lazy about validation as it stands, should probably barf if it's not a valid colour when you hit start... (the form input does get angry though)

[stylesuxx]

Admittedly a bit lazy about validation as it stands, should probably barf if it's not a valid colour when you hit start...

Would be the cleanest option, but I guess people who change that probably know what they are doing. What is the result of an invalid color? Just a black background? In this case I'd say it's fine...

[Knifa]

Yeah, it'll just be black at worst.

[stylesuxx]

Perfect, thank you! Merged.