Bug 1060541 - Add 1 additional notification to lockscreen with new music player by bug 1038723

- Also, remove the top-mask (implemented in bug 1023500) when the visually top notification in the notifications container viewport is being actioned upon.
I think it's 'build an array fulfilled with numbers from `from` to `to`. ex: range(1, 10) -> [1,2,3,...10]' ?