Add mechanism to auto-increment or decrement sliders periodically.

[lo5]

Via @FelixArokia:

TBD: should this be a part of the existing slider, or a new component?

[mturoci]

This feature is not that complex as for implementation => will not pollute core slider code so I would say adding it to an existing component is sufficient.

wdyt @lo5 ?

[lo5]

Sounds good. I'm not too excited about the little play/pause button to the bottom right. Might look better if rendered to the right of the slider, vertically aligned with the slider's track. You might have better ideas.