Convert one Dojo slider example to require.js and HTML5.

I'm opening this for discussion.  Removing the Dojo examples from Sandcastle would get us a step closer to converting them all to requireJS, which means we could eventually shed the multi-bucket system and go with baked-in require as talked about in #1747 and #1083.

The HTML5 range input works well in Chrome and FF now, but is less than optimal in IE11 (the knob is black but still works), and I haven't tested mobile.

Do we want to replace our Dojo sliders with range inputs, and drop Dojo from Sandcastle's gallery?  The payoff could someday be a button in Sandcastle that allows users to save out fully stand-alone, working examples, that they could hang on a website outside of the Sandcastle framework.