CasparCG video playout option to keep frozen last frame on signal at the end of timeline

[Sidonai-1]

When using other Caspar clients the video ends and the last frames stays frozen.

With Superconductor, you add a "new part" with just one video and the image goes to black at the end of the "part".

Obviously if the user adds blank space between items, the signal will go to black (unless there's other items, layers, etc.). I think the only real need is that the end of the timeline could stay frozen.

I think there could be a toggle/switch or something similar on the interface to have that option. I don't know if it's something that should be added on a per timeline basis or in the general config of the app, personally I cannot think of an use case for the current behavior, but if people use it that way nowadays I guess the option to choose how each timeline behaves should stay as well.

[Bohoaush]

I think this is kind of duplicate of #110