[animation] [feature request] different buttons for play/stop of animation

[Hermann-SW]

Currently there is "P" button, that does start animation as well as stops it.

Simple enhancement:

• when animation is stopped, display "P" for "play" to start animation
• when animation is running, display "S" for "stop" to stop animation

Or better use "⏯" and "⏹".

[hrgdavor]

I opted for S and P for initial implementation. somehow "⏯" and "⏹". looked uglier.

using proper icons will in a next step, the code to notify animation status and code to change button text are functioning, good enough for now.