Made some small changes to colour selection effect. The name is now, "Chroma Key : Advanced". This means more people will find it when searching.
The default option for "Operation" in "Miniumum", so that multiple alpha minuplation effects can stack.
Set the default for the delta values for 200, like it was before. in 19.04, with the 0.2 value, kdenlive just sets the values to 1000, resulting in a black image. I think this should fix it but i might be wrong.