Add explicit stop button

[BrainStone]

Describe the bug
The stop button is missing from the control bar at the bottom

To Reproduce
Steps to reproduce the behavior:

1. Open the player (make sure to (Ctrl + F5) before)
2. Check the control bar

Expected behavior
The stop button should be there. Or at least a config option for it

Screenshots

Environment details:

• OS: Windows 10
• Browser: FireFox, Chrome, Edge (embedded)
• Iris version: 3.40.0

Additional context
Issue started occuring after the update from 3.39.0

[jaedb]

To help me better understand your use case, under what normal circumstances do you need Stop instead of Pause?

[BrainStone]

Radio Stations for example struggle with the pause. So I typically stop then, so I can continue listening later.
I also use it to work around this issue: mopidy/mopidy#1704

[nilsholle]

I strongly support this request, especially for radio stations not having a stop button is quite annoying.

[arthurlutz]

I'd be interested in this too. I have a "screen" attached to my mopidy, which I automatically turn off (using node-red) when I stop, but not when I pause...

[djmattyg007]

The core track playback ended event only fires on stop, not pause. Scrobbling involves detecting the playback ended event, which never comes if you can only pause. Please add a dedicated stop button 🙏