[audio slideshow] Initial opacity for the controls

[tshort]

With the opacity set low on the player controls, it's not obvious to the user that they need to click the control to start the presentation.

It'd be nice to start the opacity at 1.0, and then switch it to the playerOpacity value after the user hits play. I got that to work locally by wedging in another CSS class that I remove after the user hits play. Someone that's better at CSS and JavaScript might know a better way.

Great plugin by the way!! ❤️