Add a Stop button to the controls

[daredoes]

Super small PR that was made easy by all the existing features and work!

Fixes #434

[jaedb]

Nice work. I would suggest the stop button is grouped with the other playback controls, rather than the mode and output controls.

A good fit would be between the Play and Next icons. A few things you will need to check is how it stacks on the various screen sizes and responsive breakpoints. To get a feel for the default breakpoints, see https://github.com/jaedb/Iris/blob/master/src/scss/global/_variables.scss#L1-L6 but note this can vary with pixel density and per-component.

[daredoes]

@jaedb The layout for the play/pause/next/previous icons is so smooth is just felt wrong to place it with them. Putting it with the other small feature icons felt more appropriate.

Maybe we can re-arrange the mode and output controls so it goes (Shuffle, Loop, Stop, Consume, Output) as to keep the shuffle and loop as close to the playback bar as possible?

Ultimately, your the creator and I will do as you suggest