Figure out a way for sliders to be longer

[ellisonbg]

When a slider has both a label and readout, the actual slider is a bit narrow. We should look at some various nice implementations of sliders (Material design, Shiny) and figure out a way so the width of our slider is never shorter than some minimum that is more reasonable.

Here is ours:

Material Design Lite:

Shiny:

https://shiny.rstudio.com/gallery/widget-gallery.html

[SylvainCorlay]

I like the idea of laying out the readout vertically.

[jasongrout]

FYI, we've thought of moving from the jqueryui slider to nouislider, which would automatically give us scales and tooltips, like in the Shiny example.

[jasongrout]

From #347, it would be great if the min and max values of the slider were displayed.