Add an "Enable/Disable All" Button

Earlier I requested that we be able to play individual parts of the sequence so that we could test to make sure each video is playing what you want it to and that the video actually works, instead of either having to watch the whole sequence while skipping to where you are wanting to test, or disabling everything and keeping your one part of the sequence enabled.

I thought that if we just have a quick "Enable/Disable All" button it would be easy to quickly disable all parts of the sequence and then go in and enable the one part you are wanting to test.  I thought this might be a good workaround if my other request (here) isn't viable.